| needle

## Function

Needleman-Wunsch global alignment

## Description

This program uses the Needleman-Wunsch global alignment algorithm to find the optimum alignment (including gaps) of two sequences when considering their entire length.

What is the optimal alignment? Dynamic programming methods ensure the optimal global alignment by exploring all possible alignments and choosing the best. It does this by reading in a scoring matrix that contains values for every possible residue or nucleotide match. Needle finds an alignment with the maximum possible score where the score of an alignment is equal to the sum of the matches taken from the scoring matrix.

### Algorithm

The Needleman-Wunsch algorithm is a member of the class of algorithms that can calculate the best score and alignment in the order of mn steps, (where 'n' and 'm' are the lengths of the two sequences). These dynamic programming algorithms were first developed for protein sequence comparison by Needleman and Wunsch, though similar methods were independently devised during the late 1960's and early 1970's for use in the fields of speech processing and computer science.

An important problem is the treatment of gaps, i.e., spaces inserted to optimise the alignment score. A penalty is subtracted from the score for each gap opened (the 'gap open' penalty) and a penalty is subtracted from the score for the total number of gap spaces multiplied by a cost (the 'gap extension' penalty).

Typically, the cost of extending a gap is set to be 5-10 times lower than the cost for opening a gap.

There are two ways to compute a penalty for a gap of n positions :

    gap opening penalty + (n - 1) * gap extension penalty
    gap penalty + n * gap length penalty

The first way is used by EMBOSS and WU-BLAST
The second way is used by NCBI-BLAST, GCG, Staden and CLUSTAL. Fasta used it for a long time the first way, but Prof. Pearson decided recently to shift to the second.

The two methods are basically equivalent.

In a Needleman-Wunsch global alignment, the entire length of each sequence is aligned. This can be thought of as an overlap between the two sequences (one can be completely within the otehr, or their ends can overlap).

This leaves no penalty for the hanging ends of the overlap. In bioinformatics, it is usually reasonable to assume that the sequences are incomplete and there should be no penalty for failing to align the missing bases.

## Usage

Here is a sample session with needle

    % needle tsw:hba_human tsw:hbb_human
    Needleman-Wunsch global alignment.
    Gap opening penalty [10.0]:
    Gap extension penalty [0.5]:
    Output alignment [hba_human.needle]:

Go to the input files for this example
Go to the output files for this example

## Command line arguments

       Standard (Mandatory) qualifiers:
      [-asequence]         sequence   Sequence USA
      [-bsequence]         seqall     Sequence database USA
       -gapopen            float      The gap open penalty is the score taken away
                                      when a gap is created. The best value
                                      depends on the choice of comparison matrix.
                                      The default value assumes you are using the
                                      EBLOSUM62 matrix for protein sequences, and
                                      the EDNAFULL matrix for nucleotide
                                      sequences.
       -gapextend          float      The gap extension, penalty is added to the
                                      standard gap penalty for each base or
                                      residue in the gap. This is how long gaps
                                      are penalized. Usually you will expect a few
                                      long gaps rather than many short gaps, so
                                      the gap extension penalty should be lower
                                      than the gap penalty. An exception is where
                                      one or both sequences are single reads with
                                      possible sequencing errors in which case you
                                      would expect many single base gaps. You can
                                      get this result by setting the gap open
                                      penalty to zero (or very low) and using the
                                      gap extension penalty to control gap
                                      scoring.
      [-outfile]           align      Output alignment file name

       Additional (Optional) qualifiers:
       -datafile           matrixf    This is the scoring matrix file used when
                                      comparing sequences. By default it is the
                                      file 'EBLOSUM62' (for proteins) or the file
                                      'EDNAFULL' (for nucleic sequences). These
                                      files are found in the 'data' directory of
                                      the EMBOSS installation.

       Advanced (Unprompted) qualifiers:
       -[no]brief          boolean    Brief identity and similarity

       Associated qualifiers:

       "-asequence" associated qualifiers
       -sbegin1             integer    Start of the sequence to be used
       -send1               integer    End of the sequence to be used
       -sreverse1           boolean    Reverse (if DNA)
       -sask1               boolean    Ask for begin/end/reverse
       -snucleotide1        boolean    Sequence is nucleotide
       -sprotein1           boolean    Sequence is protein
       -slower1             boolean    Make lower case
       -supper1             boolean    Make upper case
       -sformat1            string     Input sequence format
       -sdbname1            string     Database name
       -sid1                string     Entryname
       -ufo1                string     UFO features
       -fformat1            string     Features format
       -fopenfile1          string     Features file name

       "-bsequence" associated qualifiers
       -sbegin2             integer    Start of each sequence to be used
       -send2               integer    End of each sequence to be used
       -sreverse2           boolean    Reverse (if DNA)
       -sask2               boolean    Ask for begin/end/reverse
       -snucleotide2        boolean    Sequence is nucleotide
       -sprotein2           boolean    Sequence is protein
       -slower2             boolean    Make lower case
       -supper2             boolean    Make upper case
       -sformat2            string     Input sequence format
       -sdbname2            string     Database name
       -sid2                string     Entryname
       -ufo2                string     UFO features
       -fformat2            string     Features format
       -fopenfile2          string     Features file name

       "-outfile" associated qualifiers
       -aformat3            string     Alignment format
       -aextension3         string     File name extension
       -adirectory3         string     Output directory
       -aname3              string     Base file name
       -awidth3             integer    Alignment width
       -aaccshow3           boolean    Show accession number in the header
       -adesshow3           boolean    Show description in the header
       -ausashow3           boolean    Show the full USA in the alignment
       -aglobal3            boolean    Show the full sequence in alignment

       General qualifiers:
       -auto                boolean    Turn off prompts
       -stdout              boolean    Write standard output
       -filter              boolean    Read standard input, write standard output
       -options             boolean    Prompt for standard and additional values
       -debug               boolean    Write debug output to program.dbg
       -verbose             boolean    Report some/full command line options
       -help                boolean    Report command line options. More
                                      information on associated and general
                                      qualifiers can be found with -help -verbose
       -warning             boolean    Report warnings
       -error               boolean    Report errors
       -fatal               boolean    Report fatal errors
       -die                 boolean    Report deaths

Standard (Mandatory) qualifiers | Allowed values | Default
--- | --- | ---
[-asequence] (Parameter 1) | Sequence USA | Readable sequence | Required
[-bsequence] (Parameter 2) | Sequence database USA | Readable sequence(s) | Required
-gapopen | The gap open penalty is the score taken away when a gap is created. The best value depends on the choice of comparison matrix. The default value assumes you are using the EBLOSUM62 matrix for protein sequences, and the EDNAFULL matrix for nucleotide sequences. | Floating point number from 1.0 to 100.0 | 10.0 for any sequence
-gapextend | The gap extension, penalty is added to the standard gap penalty for each base or residue in the gap. This is how long gaps are penalized. Usually you will expect a few long gaps rather than many short gaps, so the gap extension penalty should be lower than the gap penalty. An exception is where one or both sequences are single reads with possible sequencing errors in which case you would expect many single base gaps. You can get this result by setting the gap open penalty to zero (or very low) and using the gap extension penalty to control gap scoring. | Floating point number from 0.0 to 10.0 | 0.5 for any sequence
[-outfile] (Parameter 3) | Output alignment file name | Alignment output file |
Additional (Optional) qualifiers | Allowed values | Default
-datafile | This is the scoring matrix file used when comparing sequences. By default it is the file 'EBLOSUM62' (for proteins) or the file 'EDNAFULL' (for nucleic sequences). These files are found in the 'data' directory of the EMBOSS installation. | Comparison matrix file in EMBOSS data path | EBLOSUM62 for protein EDNAFULL for DNA
Advanced (Unprompted) qualifiers | Allowed values | Default
-[no]brief | Brief identity and similarity | Boolean value Yes/No | Yes

## Input file format

needle reads any 2 sequence USAs of the same type (DNA or protein).

### Input files for usage example

'tsw:hba_human' is a sequence entry in the example protein database 'tsw'

### Database entry: tsw:hba_human

    ID   HBA_HUMAN      STANDARD;      PRT;   141 AA.
    AC   P01922;
    DT   21-JUL-1986 (Rel. 01, Created)
    DT   21-JUL-1986 (Rel. 01, Last sequence update)
    DT   15-JUL-1999 (Rel. 38, Last annotation update)
    DE   HEMOGLOBIN ALPHA CHAIN.
    GN   HBA1 AND HBA2.
    OS   Homo sapiens (Human), Pan troglodytes (Chimpanzee), and
    OS   Pan paniscus (Pygmy chimpanzee) (Bonobo).
    OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Mammalia;
    OC   Eutheria; Primates; Catarrhini; Hominidae; Homo.
    RN   [1]
    RP   SEQUENCE FROM N.A. (ALPHA-1).
    RX   MEDLINE; 81088339.
    RA   MICHELSON A.M., ORKIN S.H.;
    RT   "The 3' untranslated regions of the duplicated human alpha-globin
    RT   genes are unexpectedly divergent.";
    RL   Cell 22:371-377(1980).
    RN   [2]
    RP   SEQUENCE FROM N.A. (ALPHA-2).
    RX   MEDLINE; 81175088.
    RA   LIEBHABER S.A., GOOSSENS M.J., KAN Y.W.;
    RT   "Cloning and complete nucleotide sequence of human 5'-alpha-globin
    RT   gene.";
    RL   Proc. Natl. Acad. Sci. U.S.A. 77:7054-7058(1980).
    RN   [3]
    RP   SEQUENCE FROM N.A. (ALPHA-2).
    RX   MEDLINE; 80137531.
    RA   WILSON J.T., WILSON L.B., REDDY V.B., CAVALLESCO C., GHOSH P.K.,
    RA   DERIEL J.K., FORGET B.G., WEISSMAN S.M.;
    RT   "Nucleotide sequence of the coding portion of human alpha globin
    RT   messenger RNA.";
    RL   J. Biol. Chem. 255:2807-2815(1980).
    RN   [4]
    RP   SEQUENCE FROM N.A. (ALPHA-1 AND ALPHA-2).
    RA   FLINT J., HIGGS D.R.;
    RL   Submitted (JAN-1997) to the EMBL/GenBank/DDBJ databases.
    RN   [5]
    RP   SEQUENCE.
    RA   BRAUNITZER G., GEHRING-MULLER R., HILSCHMANN N., HILSE K., HOBOM G.,
    RA   RUDLOFF V., WITTMANN-LIEBOLD B.;
    RT   "The constitution of normal adult human haemoglobin.";
    RL   Hoppe-Seyler's Z. Physiol. Chem. 325:283-286(1961).
    RN   [6]
    RP   SEQUENCE.
    RA   HILL R.J., KONIGSBERG W.;
    RT   "The structure of human hemoglobin: IV. The chymotryptic digestion of
    RT   the alpha chain of human hemoglobin.";
    RL   J. Biol. Chem. 237:3151-3156(1962).
    RN   [7]

      [Part of this file has been deleted for brevity]

    FT                                /FTId=VAR_002841.
    FT   VARIANT     130    130       A -> D (IN YUDA; O2 AFFINITY DOWN).
    FT                                /FTId=VAR_002842.
    FT   VARIANT     131    131       S -> P (IN QUESTEMBERT; HIGHLY UNSTABLE;
    FT                                CAUSES ALPHA-THALASSEMIA).
    FT                                /FTId=VAR_002843.
    FT   VARIANT     133    133       S -> R (IN VAL DE MARNE; O2 AFFINITY UP).
    FT                                /FTId=VAR_002844.
    FT   VARIANT     135    135       V -> E (IN PAVIE).
    FT                                /FTId=VAR_002845.
    FT   VARIANT     136    136       L -> M (IN CHICAGO).
    FT                                /FTId=VAR_002846.
    FT   VARIANT     136    136       L -> P (IN BIBBA; UNSTABLE;
    FT                                CAUSES ALPHA-THALASSEMIA).
    FT                                /FTId=VAR_002847.
    FT   VARIANT     138    138       S -> P (IN ATTLEBORO; O2 AFFINITY UP).
    FT                                /FTId=VAR_002848.
    FT   VARIANT     139    139       K -> E (IN HANAKAMI; O2 AFFINITY UP).
    FT                                /FTId=VAR_002849.
    FT   VARIANT     139    139       K -> T (IN TOKONAME; O2 AFFINITY UP).
    FT                                /FTId=VAR_002850.
    FT   VARIANT     140    140       Y -> H (IN ROUEN; O2 AFFINITY UP).
    FT                                /FTId=VAR_002851.
    FT   VARIANT     141    141       R -> C (IN NUNOBIKI; O2 AFFINITY UP).
    FT                                /FTId=VAR_002852.
    FT   VARIANT     141    141       R -> L (IN LEGNANO; O2 AFFINITY UP).
    FT                                /FTId=VAR_002853.
    FT   VARIANT     141    141       R -> H (IN SURESNES; O2 AFFINITY UP).
    FT                                /FTId=VAR_002854.
    FT   VARIANT     141    141       R -> P (IN SINGAPORE).
    FT                                /FTId=VAR_002855.
    FT   HELIX         4     35
    FT   HELIX        37     42
    FT   TURN         44     45
    FT   TURN         50     51
    FT   HELIX        53     71
    FT   TURN         72     74
    FT   HELIX        76     79
    FT   TURN         80     80
    FT   HELIX        81     89
    FT   TURN         90     91
    FT   TURN         95     95
    FT   HELIX        96    112
    FT   TURN        114    116
    FT   HELIX       119    136
    FT   TURN        137    139
    SQ   SEQUENCE   141 AA;  15126 MW;  5EC7DB1E CRC32;
         VLSPADKTNV KAAWGKVGAH AGEYGAEALE RMFLSFPTTK TYFPHFDLSH GSAQVKGHGK
         KVADALTNAV AHVDDMPNAL SALSDLHAHK LRVDPVNFKL LSHCLLVTLA AHLPAEFTPA
         VHASLDKFLA SVSTVLTSKY R
    //

### Database entry: tsw:hbb_human

    ID   HBB_HUMAN      STANDARD;      PRT;   146 AA.
    AC   P02023;
    DT   21-JUL-1986 (Rel. 01, Created)
    DT   21-JUL-1986 (Rel. 01, Last sequence update)
    DT   15-JUL-1999 (Rel. 38, Last annotation update)
    DE   HEMOGLOBIN BETA CHAIN.
    GN   HBB.
    OS   Homo sapiens (Human), Pan troglodytes (Chimpanzee), and
    OS   Pan paniscus (Pygmy chimpanzee) (Bonobo).
    OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Mammalia;
    OC   Eutheria; Primates; Catarrhini; Hominidae; Homo.
    RN   [1]
    RP   SEQUENCE.
    RC   SPECIES=HUMAN;
    RA   BRAUNITZER G., GEHRING-MULLER R., HILSCHMANN N., HILSE K., HOBOM G.,
    RA   RUDLOFF V., WITTMANN-LIEBOLD B.;
    RT   "The constitution of normal adult human haemoglobin.";
    RL   Hoppe-Seyler's Z. Physiol. Chem. 325:283-286(1961).
    RN   [2]
    RP   SEQUENCE FROM N.A.
    RC   SPECIES=HUMAN;
    RX   MEDLINE; 81064667.
    RA   LAWN R.M., EFSTRATIADIS A., O'CONNELL C., MANIATIS T.;
    RT   "The nucleotide sequence of the human beta-globin gene.";
    RL   Cell 21:647-651(1980).
    RN   [3]
    RP   SEQUENCE OF 121-146 FROM N.A.
    RC   SPECIES=HUMAN;
    RX   MEDLINE; 85205333.
    RA   LANG K.M., SPRITZ R.A.;
    RT   "Cloning specific complete polyadenylylated 3'-terminal cDNA
    RT   segments.";
    RL   Gene 33:191-196(1985).
    RN   [4]
    RP   X-RAY CRYSTALLOGRAPHY (2.5 ANGSTROMS) OF DEOXYHEMOGLOBIN.
    RC   SPECIES=HUMAN;
    RX   MEDLINE; 76027820.
    RA   FERMI G.;
    RT   "Three-dimensional fourier synthesis of human deoxyhaemoglobin at
    RT   2.5-A resolution: refinement of the atomic model.";
    RL   J. Mol. Biol. 97:237-256(1975).
    RN   [5]
    RP   SEQUENCE.
    RC   SPECIES=P.TROGLODYTES;
    RX   MEDLINE; 66071496.
    RA   RIFKIN D.B., KONIGSBERG W.;
    RT   "The characterization of the tryptic peptides from the hemoglobin of
    RT   the chimpanzee (Pan troglodytes).";
    RL   Biochim. Biophys. Acta 104:457-461(1965).
    RN   [6]

      [Part of this file has been deleted for brevity]

    FT   VARIANT     140    140       A -> T (IN ST JACQUES: O2 AFFINITY UP).
    FT                                /FTId=VAR_003081.
    FT   VARIANT     140    140       A -> V (IN PUTTELANGE; POLYCYTHEMIA;
    FT                                O2 AFFINITY UP).
    FT                                /FTId=VAR_003082.
    FT   VARIANT     141    141       L -> R (IN OLMSTED; UNSTABLE).
    FT                                /FTId=VAR_003083.
    FT   VARIANT     142    142       A -> D (IN OHIO; O2 AFFINITY UP).
    FT                                /FTId=VAR_003084.
    FT   VARIANT     143    143       H -> D (IN RANCHO MIRAGE).
    FT                                /FTId=VAR_003085.
    FT   VARIANT     143    143       H -> Q (IN LITTLE ROCK; O2 AFFINITY UP).
    FT                                /FTId=VAR_003086.
    FT   VARIANT     143    143       H -> P (IN SYRACUSE; O2 AFFINITY UP).
    FT                                /FTId=VAR_003087.
    FT   VARIANT     143    143       H -> R (IN ABRUZZO; O2 AFFINITY UP).
    FT                                /FTId=VAR_003088.
    FT   VARIANT     144    144       K -> E (IN MITO; O2 AFFINITY UP).
    FT                                /FTId=VAR_003089.
    FT   VARIANT     145    145       Y -> C (IN RAINIER; O2 AFFINITY UP).
    FT                                /FTId=VAR_003090.
    FT   VARIANT     145    145       Y -> H (IN BETHESDA; O2 AFFINITY UP).
    FT                                /FTId=VAR_003091.
    FT   VARIANT     146    146       H -> D (IN HIROSHIMA; O2 AFFINITY UP).
    FT                                /FTId=VAR_003092.
    FT   VARIANT     146    146       H -> L (IN COWTOWN; O2 AFFINITY UP).
    FT                                /FTId=VAR_003093.
    FT   VARIANT     146    146       H -> P (IN YORK; O2 AFFINITY UP).
    FT                                /FTId=VAR_003094.
    FT   VARIANT     146    146       H -> Q (IN KODAIRA; O2 AFFINITY UP).
    FT                                /FTId=VAR_003095.
    FT   HELIX         5     15
    FT   TURN         16     17
    FT   HELIX        20     34
    FT   HELIX        36     41
    FT   HELIX        43     45
    FT   HELIX        51     55
    FT   TURN         56     56
    FT   HELIX        58     75
    FT   TURN         76     77
    FT   HELIX        78     94
    FT   TURN         95     96
    FT   TURN        100    100
    FT   HELIX       101    121
    FT   HELIX       124    142
    FT   TURN        143    144
    SQ   SEQUENCE   146 AA;  15867 MW;  EC9744C9 CRC32;
         VHLTPEEKSA VTALWGKVNV DEVGGEALGR LLVVYPWTQR FFESFGDLST PDAVMGNPKV
         KAHGKKVLGA FSDGLAHLDN LKGTFATLSE LHCDKLHVDP ENFRLLGNVL VCVLAHHFGK
         EFTPPVQAAY QKVVAGVANA LAHKYH
    //

## Output file format

The output is a standard EMBOSS alignment file.

The results can be output in one of several styles by using the command-line qualifier -aformat xxx, where 'xxx' is replaced by the name of the required format. Some of the alignment formats can cope with an unlimited number of sequences, while others are only for pairs of sequences.

The available multiple alignment format names are: unknown, multiple, simple, fasta, msf, trace, srs

The available pairwise alignment format names are: pair, markx0, markx1, markx2, markx3, markx10, srspair, score

See: http://emboss.sf.net/docs/themes/AlignFormats.html for further information on alignment formats.

### Output files for usage example

### File: hba_human.needle

    ########################################
    # Program: needle
    # Rundate: Thu Jul 15 2004 12:00:00
    # Align_format: srspair
    # Report_file: hba_human.needle
    ########################################

    #=======================================
    #
    # Aligned_sequences: 2
    # 1: HBA_HUMAN
    # 2: HBB_HUMAN
    # Matrix: EBLOSUM62
    # Gap_penalty: 10.0
    # Extend_penalty: 0.5
    #
    # Length: 148
    # Identity:      63/148 (42.6%)
    # Similarity:    88/148 (59.5%)
    # Gaps:           9/148 ( 6.1%)
    # Score: 290.5
    #
    #
    #=======================================

    HBA_HUMAN          1 -VLSPADKTNVKAAWGKVGAHAGEYGAEALERMFLSFPTTKTYFPHF-DL     48
                          .|:|.:|:.|.|.||||  :..|.|.|||.|:.:.:|.|:.:|..| ||
    HBB_HUMAN          1 VHLTPEEKSAVTALWGKV--NVDEVGGEALGRLLVVYPWTQRFFESFGDL     48

    HBA_HUMAN         49 S-----HGSAQVKGHGKKVADALTNAVAHVDDMPNALSALSDLHAHKLRV     93
                         |     .|:.:||.|||||..|.::.:||:|::....:.||:||..||.|
    HBB_HUMAN         49 STPDAVMGNPKVKAHGKKVLGAFSDGLAHLDNLKGTFATLSELHCDKLHV     98

    HBA_HUMAN         94 DPVNFKLLSHCLLVTLAAHLPAEFTPAVHASLDKFLASVSTVLTSKYR    141
                         ||.||:||.:.|:..||.|...||||.|.|:..|.:|.|:..|..||.
    HBB_HUMAN         99 DPENFRLLGNVLVCVLAHHFGKEFTPPVQAAYQKVVAGVANALAHKYH    146

    #---------------------------------------
    #---------------------------------------

The Identity: is the percentage of identical matches between the two sequences over the reported aligned region (including any gaps in the length).

The Similarity: is the percentage of matches between the two sequences over the reported aligned region (including any gaps in the length).

## Data files

For protein sequences EBLOSUM62 is used for the substitution matrix. For nucleotide sequence, EDNAFULL is used. Others can be specified.

EMBOSS data files are distributed with the application and stored in the standard EMBOSS data directory, which is defined by the EMBOSS environment variable EMBOSS_DATA.

To see the available EMBOSS data files, run:

    % embossdata -showall

To fetch one of the data files (for example 'Exxx.dat') into your current directory for you to inspect or modify, run:

    % embossdata -fetch -file Exxx.dat

Users can provide their own data files in their own directories. Project specific files can be put in the current directory, or for tidier directory listings in a subdirectory called ".embossdata". Files for all EMBOSS runs can be put in the user's home directory, or again in a subdirectory called ".embossdata".

The directories are searched in the following order:

- . (your current directory)
- .embossdata (under your current directory)
- ~/ (your home directory)
- ~/.embossdata

## Notes

needle is a true implementation of the Needleman-Wunsch algorithm and so produces a full path matrix. It therefore cannot be used with genome sized sequences unless you've a lot of memory and a lot of time.

## References

1. Needleman, S. B. and Wunsch, C. D. (1970) J. Mol. Biol. 48, 443-453.
2. Kruskal, J. B. (1983) An overview of squence comparison In D. Sankoff and J. B. Kruskal, (ed.), Time warps, string edits and macromolecules: the theory and practice of sequence comparison, pp. 1-44 Addison Wesley.

## Warnings

needle is for aligning two sequences over their entire length. This works best with closely related sequences. If you use needle to align very distantly-related sequences, it will produce a result but much of the alignment may have little or no biological significance.

A true Needleman Wunsch implementation like needle needs memory proportional to the product of the sequence lengths. For two sequences of length 10,000,000 and 1,000 it therefore needs memory proportional to 10,000,000,000 characters. Two arrays of this size are produced, one of ints and one of floats so multiply that figure by 8 to get the memory usage in bytes. That doesn't include other overheads. Therefore only use water and needle for accurate alignment of reasonably short sequences.

If you run out of memory, try using stretcher instead.

## Diagnostic Error Messages

    Uncaught exception
     Assertion failed
     raised at ajmem.c:xxx

Probably means you have run out of memory. Try using stretcher if this happens.

## Exit status

0 upon successful completion.

## Known bugs

None.

## See also

Program name | Description
--- | ---
est2genome | Align EST and genomic DNA sequences
stretcher | Finds the best global alignment between two sequences

When you want an alignment that covers the whole length of both sequences, use needle.

When you are trying to find the best region of similarity between two sequences, use water.

stretcher is a more suitable program to use to find global alignments of very long sequences.

## Author(s)

Alan Bleasby (ableasby © rfcgr.mrc.ac.uk)
MRC Rosalind Franklin Centre for Genomics Research Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SB, UK

## History

Completed 8th July 1999.

Modified 26th July 1999 - scoring tweaked.

Modified 22 Oct 2000 - %ID and %Similarity scores added.

## Target users

This program is intended to be used by everyone and everything, from naive users to embedded scripts.

## Comments

None