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NCBI BLAST+ (Vectors Databases)

Introduction

BLAST stands for Basic Local Alignment Search Tool.The emphasis of this tool is to find regions of sequence similarity, which will yield functional and evolutionary clues about the structure and function of your sequence.

Official Website
Download Software

How to use this tool

Running a tool from the web form is a simple multiple steps process, starting at the top of the page and following the steps to the bottom.

Each tool has at least 2 steps, but most of them have more:

  • The first steps are usually where the user sets the tool input (e.g. sequences, databases...)
  • In the following steps, the user has the possibility to change the default tool parameters
  • And finally, the last step is always the tool submission step, where the user can specify a title to be associated with the results and an email address for email notification. Using the submit button will effectively submit the information specified previously in the form to launch the tool on the server

Note that the parameters are validated prior to launching the tool on the server and in the event of a missing or wrong combination of parameters, the user will be notified directly in the form.

Step 1 - Database

Databases

Database

Database Name Description Abbreviation
emvec emvec

Default value is: emvec

Step 2 - Sequence

Sequence Input Window

The query sequence can be entered directly into this form. The sequence can be in GCG, FASTA, EMBL, GenBank, PIR, NBRF, PHYLIP or UniProtKB/Swiss-Prot format. A partially formatted sequence is not accepted. Adding a return to the end of the sequence may help certain applications understand the input. Note that directly using data from word processors may yield unpredictable results as hidden/control characters may be present.

Sequence File Upload

A file containing a valid sequence in any format (GCG, FASTA, EMBL, GenBank, PIR, NBRF, PHYLIP or UniProtKB/Swiss-Prot) can be used as input for the sequence similarity search. Word processors files may yield unpredictable results as hidden/control characters may be present in the files. It is best to save files with the Unix format option to avoid hidden Windows characters.

Sequence Type

Indicates if the sequence is protein or DNA/RNA.

Type Abbreviation
PROTEIN protein
DNA/RNA dna

Default value is: DNA/RNA [dna]

Step 3 - Parameters

Program

The BLAST program to be used for the Sequence Similarity Search.

Program Name Description Abbreviation
blastn Compares a nucleotide sequence (DNA/RNA) to a nucleotide sequence database blastn
tblastx Compares the six-frame translations of a nucleotide query sequence against the six-frame translations of a nucleotide sequence database. Please note that TBLASTX is extremely slow and cpu-intensive. tblastx
tblastn Compares a protein query sequence against a nucleotide sequence database dynamically translated in all reading frames. tblastn

Default value is: blastn

Task

Task option (only selectable for blastn)

Task Name Description Abbreviation
blastn Traditional BLASTN task blastn
megablast Megablast task for quickly searching very similar (e.g., intraspecies or closely related species) sequences megablast

Default value is: blastn

Matrix

(Protein searches) The substitution matrix used for scoring alignments when searching the database.

Matrix Name Abbreviation
BLOSUM45 BLOSUM45
BLOSUM50 BLOSUM50
BLOSUM62 BLOSUM62
BLOSUM80 BLOSUM80
BLOSUM90 BLOSUM90
PAM30 PAM30
PAM70 PAM70
PAM250 PAM250

Default value is: BLOSUM62

Additional information

Match/mismatch_scores

(Nucleotide searches) The match score is the bonus to the alignment score when matching the same base. The mismatch is the penalty when failing to match.

Match/mismatch_scores Name Abbreviation
1,-4 1,-4
2,-7 2,-7
1,-3 1,-3
2,-5 2,-5
1,-2 1,-2
2,-3 2,-3
1,-1 1,-1
5,-4 5,-4
4,-5 4,-5

Default value is: 1,-3

Gap Open Penalty

Penalty taken away from the score when a gap is created in sequence. Increasing the gap openning penalty will decrease the number of gaps in the final alignment.

Default value is: default [-1]

Additional information

Gap Extend Penalty

Penalty taken away from the score for each base or residue in the gap. Increasing the gap extension penalty favors short gaps in the final alignment, conversly decreasing the gap extension penalty favors long gaps in the final alignment.

Default value is: default [-1]

Additional information

Gap Align

This is a true/false setting that tells the program the perform optimised alignments within regions involving gaps. If set to true, the program will perform an alignment using gaps. Otherwise, if it is set to false, it will report only individual HSP where two sequence match each other, and thus will not produce alignments with gaps.

Default value is: true

Additional information

Expectation Threshold

Limits the number of scores and alignments reported based on the expectation value. This is the maximum number of times the match is expected to occur by chance.

Default value is: 10 (default) [10]

Filter

Filter regions of low sequence complexity. This can avoid issues with low complexity sequences where matches are found due to composition rather than meaningful sequence similarity. However in some cases filtering also masks regions of interest and so should be used with caution.

Default value is: yes [T]

Dropoff

The amount a score can drop before gapped extension of word hits is halted

Default value is: 0 (default) [0]

Scores

Maximum number of match score summaries reported in the result output.

Default value is: 50 (default) [50]

Alignments

Maximum number of match alignments reported in the result output.

Default value is: 50 (default) [50]

Sequence Range

Specify a range or section of the input sequence to use in the search. Example: Specifying '34-89' in an input sequence of total length 100, will tell BLAST to only use residues 34 to 89, inclusive.

Default value is: START-END

Alignment Views

Formating for the alignments

Name Description Value
pairwise The query and match are output as a pairwsie alignment with a consensus line between the two sequences. In the consensus the match states are represented as: identical match as the base/residue, similarity as a '+' and missmatch as a space. 0
Query-anchored identities The matches found are shown relative to the ungapped query sequence as a differences to the query. Identities appear as dots (.), similarites in upper case, missmatches in lower case and gaps as dash (-). Insertions are indictated with a line pointing to the insertion site with the inserted sequence on another line. 1
Query-anchored non-identities The matches found are shown relative to the ungapped query sequence as a differences to the query. Identities and similarites appear in upper case, missmatches in lower case and gaps as dash (-). Insertions are indictated with a line pointing to the insertion site with the inserted sequence on another line. 2
Flat query-anchored identities The matches found are shown relative to the gapped query sequence as a differences to the query. Identities appear as dots (.), similarites in upper case, missmatches in lower case and gaps as dash (-). 3
Flat query-anchored non-identities The matches found are shown relative to the gapped query sequence as a differences to the query. Identities and similarites appear in upper case, missmatches in lower case and gaps as dash (-). 4
BLASTXML Output NCBI BLAST XML instead of a plain text report. 5
tabular Summary output in tabular format. 6
tabular with comment lines Summary output in tabular format. 7
Text ASN.1 Output in ASN.1 format. 8
Binary ASN.1 Output in ASN.1 format. 9
Comma-separated values Summary output as comma separated values. 10
BLAST archive format (ASN.1) Output in BLAST archive format (ASN.1). 11

Default value is: pairwise [0]

Composition-based Statistics

Use composition-based statistics.

Name Description Value
F (default) No composition-based statistics F
D (equivalent to 2) D
1 Composition-based statistics as in NAR 29:2994-3005, 2001 1
2 Composition-based score adjustment as in Bioinformatics 21:902-911,2005, conditioned on sequence properties 2
3 Composition-based score adjustment as in Bioinformatics 21:902-911, 2005, unconditionally 3

Default value is: F (default) [F]

Translation Table

Query Genetic code to use in translation

Name Value
N/A -1
Standard SGC0 1
Vertebrate Mitochondrial 2
Yeast Mitochondrial 3
Mold Mitochondrial Protozoan Mitochondrial Coelenterate 4
Invertebrate Mitochondrial 5
Ciliate Nuclear Dasycladacean Nuclear Hexamita Nuclear 6
Echinoderm Mitochondrial Flatworm Mitochondrial 9
Euplotid Nuclear 10
Bacterial and Plant Plastid 11
Alternative Yeast Nuclear 12
Ascidian Mitochondrial 13
Alternative Flatworm Mitochondrial 14
Blepharisma Macronuclear 15
Chlorophycean Mitochondrial 16
Trematode Mitochondrial 21
Scenedesmus obliquus Mitochondrial 22
Thraustochytrium Mitochondrial 23

Default value is: Standard SGC0 [1]

Step 4 - Submission

Job title

It's possible to identify the tool result by giving it a name. This name will be associated to the results and might appear in some of the graphical representations of the results.

Email Notification

Running a tool is usually an interactive process, the results are delivered directly to the browser when they become available. Depending on the tool and its input parameters, this may take quite a long time. It's possible to be notified by email when the job is finished by simply ticking the box "Be notified by email". An email with a link to the results will be sent to the email address specified in the corresponding text box. Email notifications require valid email addresses.

Email Address

If email notification is requested, then a valid Internet email address in the form joe@example.org must be provided. This is not required when running the tool interactively (The results will be delivered to the browser window when they are ready).

References

BLAST+: architecture and applications.
(2009 December 15) BMC bioinformatics 10 :421
Gapped BLAST and PSI-BLAST: a new generation of protein database search programs.
(1997 September 01) Nucleic acids research 25 (17) :3389-402
Basic local alignment search tool.
(1990 October 05) Journal of molecular biology 215 (3) :403-10
The EMBL-EBI bioinformatics web and programmatic tools framework.
(2015 July 01) Nucleic acids research 43 (W1) :W580-4
Analysis Tool Web Services from the EMBL-EBI.
(2013 July) Nucleic acids research 41 (Web Server issue) :W597-600