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ExPASy Logo TagIdent tool (formerly GuessProt)

TagIdent is a tool which allows
  1. the generation of a list of proteins close to a given pI and Mw,
  2. the identification of proteins by matching a short sequence tag of up to 6 amino acids against proteins in the Swiss-Prot/TrEMBL databases close to a given pI and Mw,
  3. the identification of proteins by their mass, if this mass has been determined by mass spectrometric techniques
for one or more species and with an optional keyword [references].
Documentation is available.
Fill out in the following form the pI (isoelectric point) and Mw (molecular weight) you want the search to focus on. The pI and Mw ranges allow you to specify the intervals of pI and Mw values in which the search should take place.

The OS or OC (Organism Species or Organism Classfication) field allows you to specify terms to limit the search to a range of organisms or to a specific organism (species). A Swiss-Prot/TrEMBL entry will only be returned, if all the given terms appear in either the OS or OC lines of that entry. If in doubt, please consult the Swiss-Prot list of species.

Scan in Swiss-Prot can be restricted by the use of a keyword. This should be a keyword in the Swiss-Prot KW lines. If in doubt, consult the Swiss-Prot list of keywords.

For example, entering the following values:

pI = 5.4
Mw = 35000
pI range = 0.25
Mw range = 20%
OS or OC = planta
Keyword = chloroplast
will return all Swiss-Prot entries for plant chloroplast proteins, with 5.15 <= pI <= 5.65 and 28000 <= Mw <= 42000.

When searching in Swiss-Prot, TagIdent removes signal sequences and/or propeptides (as documented in the Swiss-Prot feature table (FT lines)) before computing pI and Mw for each of the resulting chains.

The annotation in TrEMBL is done automatically; it is incomplete and not always correct. Thus information on TrEMBL FT lines is not used to process TrEMBL proteins into mature chains or peptides (i.e. pI and Mw are always computed for the whole sequence), and the use of a keyword is not allowed for searches in TrEMBL.

Name of your query (optional):
pI: pI range:
Mw (in Daltons, not kD): Mw range (in percent): .

OS or OC:

Keyword from KW lines (for search in Swiss-Prot only):

With this option, the first 40 amino acids (or the last 40 aa or the matching internal subsequence) of each protein are printed in the result, in addition to the protein name. You may optionally also enter a tag which will be matched with the sequences. If the tag is found in the displayed sequence, it will be shown in lower case, and the numerical position of the tag in the protein will be given. 'X' can be used to mean 'any amino acid'.
Tag (up to 6 amino acids):

Search for all possible tag permutations.

Display only the sequences matching the tag.

Include scan of your tag against all fragments in Swiss-Prot/TrEMBL matching your OS/OC (and KW terms for Swiss-Prot only). Note: pI and Mw are not computed for fragments.

Display the predicted N-terminal sequence or the C-terminal sequence or the (internal) area of the protein that matches your tag.

Send the result by e-mail
With this option, you will receive the result by e-mail.
Your e-mail:

Database(s) on which the scan should be performed:
Swiss-Prot and TrEMBL
To run the search: or

Last modified 27/Jan/2003 by ELG
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