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PRATT version 2.1 Documentation

Written by:
Inge Jonassen,

Created: February 7th 1997


  1. What is Pratt?
    • 1.1 References
    • 1.2 Pattern terminology
  2. User manual.
    • 2.1 Format of input sequences.
    • 2.2 Command line.
    • 2.3 Using the menu to control your search.
      • The menu.
    • 2.4 Controlling the search via command line options.
    • 2.5 Recommendation.
  3. Technical details.

New features in version 2.1:

2.0 was the last major version of Pratt, in the 2.1 version only minor things have been added/changed. A few bugs in version 2.0 have been fixed in 2.1. Inge Jonassen is grateful to Dr. John F. Collins, University of Edinburgh, who proposed many of the added features, and discovered many of the bugs.

What was new in version 2.0?

In addition to the set S of protein sequences, the user can input: Branch-and-bound and heuristics have been added to make the pattern search more efficient. The speed-up is significant, in particular for sets of relatively similar (closely related) sequences.

Pratt has integrated new pattern scoring mechanisms, including one taking into account the diversity of the sequences matching a pattern, and another taking into account the number of sequences matching each pattern.

1. What is Pratt?

Pratt is a tool that allows the user to search for patterns conserved in a set of protein sequences. The user can specify what kind of patterns should be searched for, and how many sequences should match a pattern to be reported.

1.1 References:

  1. Finding flexible patterns in unaligned protein sequences.
    Inge Jonassen, John F. Collins, Desmond Higgins.
    Protein Science 1995;4(8):1587-1595.
  2. Efficient discovery of conserved patterns using a pattern graph.
    Inge Jonassen.
    Submitted to CABIOS.
  3. Scoring function for pattern discovery programs taking into account sequence diversity.
    Inge Jonassen, Carsten Helgesen, Desmond Higgins.
    Dept. of Informatics, Univ. of Bergen, Reports in Informatics no 116, Febr. 1996.
  4. Discovering patterns and subfamilies in biosequences.
    A. Brazma, I. Jonassen, E. Ukkonen, and J. Vilo.
    in Proceedings of the Fourth International Conference on Intellignent Systems for Molecular Biology (ISMB-96), AAAI Press 1996, p 34-43.

1.2 Pattern terminology

Pratt is able to discover conserved patterns in the sequences.

The patterns that can be found is a subset of the set of patterns that can be described using Prosite notation.

A pattern that can be found by Pratt can be written on the form


where The product of flexibility for a pattern is the product of the flexibilities of the flexible wildcard regions in the pattern, if any, otherwise it is defined to be one.


  1. C-x(2)-H is a pattern with two components (C and H) and one fixed wildcard region. It matches any sequence containing a C followed by any two arbitrary amino acids followed by an H. For example aaChgHyw and liChgHlyw.
  2. C-x(2,3)-H is a pattern with two components (C and H) and one flexible wildcard region. It matches any sequence containing a C followed by any two or three arbitrary amino acids followed by an H. For example aaChgHywk and liChgaHlyw.
  3. C-x(2,3)-[ILV] is a pattern with two components (C and [ILV]) and one flexible wildcard region. It matches any sequence containing a C followed by any two or three arbitrary amino acids followed by an I, L or V.

2. User manual

2.1 Format of input sequences.

Make a file or a set of files containing the set of sequences to be analysed. Currently, Pratt can read one of the formats:

2.2 Command line.

Command line:
    Pratt <format> <filename> [options]
where <format> is one of: and <filename> is the name of a file containing the sequences in the given format

2.3 Using the menu to control your search.

When you run Pratt, it will give you a menu allowing you to set a variety of parameters controlling:
  1. what kind of patterns Pratt is going to look for,
  2. how many sequences a pattern should match,
  3. lower threshold on significance for a pattern to be reported, and
  4. how many patterns should be reported.
  5. greediness in search (new in version 2.0)
  6. if a query sequence or an alignment is to be used (new in version 2.0)
  7. if a pattern is restricted to match within a specified region in one or several of the sequences (new in version 2.1).

Schematic figure of algorithm used in Pratt version 2.x

Overview of the pattern discovery algorithm. The user inputs a set unaligned sequences, and the minimum number of sequences to match a pattern. (i): During this phase, patterns are constrained to the pattern class defined by the bounds set using the menu. A pattern graph can be constructed either from the shortest sequences in S (1), from a special query sequence (2), or from a multiple sequence alignment (3). A search is done for the highest scoring patterns in the class that can be derived from the pattern graph. The block data structure is used to find all matches to each pattern. (ii): The highest scoring patterns found during this search, are input to a heuristic pattern refinement algorithm, where more ambiguous pattern components (from a list given by the user in Pratt.sets) can be added to the patterns found during phase (i). The refinement phase is optional.

Sample run of Pratt version 2.1:


                Pratt version 2.1, Sept. 1996

                 Written by Inge Jonassen, 

                   University of Bergen


                   email: inge@ii.uib.no

                 For more information, see 



                        Please quote:

             I.Jonassen, J.F.Collins, D.G.Higgins.

             Protein Science 1995;4(8):1587-1595.


                     submitted to CABIOS 





                Pratt version 2.1 


        Analysing 166 sequences from file snake



   CM: min Nr of Seqs to Match                166

   C%: min Percentage Seqs to Match         100.0



   PP: pos in seq [off,complete,start]        off

   PL: max Pattern Length                      50

   PN: max Nr of Pattern Symbols               50

   PX: max Nr of consecutive x's                5

   FN: max Nr of flexible spacers               2

   FL: max Flexibility                          2

   FP: max Flex.Product                        10

   BI: Input Pattern Symbol File              off

   BN: Nr of Pattern Symbols Initial Search    20



   S: Scoring [info,mdl,tree,dist,ppv]       info



   G: Pattern Graph from [seq,al,query]       seq

   E: Search Greediness                         3

   R: Pattern Refinement                       on

   RG: Generalise ambiguous symbols           off



   OF: Output Filename              snake.166.pat

   OP: PROSITE Pattern Format                  on

   ON: max number patterns                     50

   OA: max number Alignments                   50

   M: Print Patterns in sequences              on

   MR: ratio for printing                      10

   MV: print vertically                       off



X: eXecute program

Q: Quit


help: for on-line help



C Options:
The C parameters control how many sequences a pattern should match to be considered by Pratt:
Set the minimum number of sequences to match a pattern. Pratt will only report patterns that match at least the chosen number of the sequences that you have input. Pratt will not allow you to choose a value higher than the number of sequences input.
set the minimum percentage of the input sequences that should match a pattern. If you set this to, say 80, Pratt will only report patterns matching at least 80 % of the sequences input.

G Options:
Allows the use of an alignment or a query sequence to restrict the pattern search.

If G is set to al or query, another option GF will appear allowing the user to give the name of a file containing a multiple sequence alignment (in Clustal W format), or a query sequence in FastA format (without annotation).n Only patterns consistent with the alignment/matching the query sequence will be considered.

Loosely a pattern is considered consistent with the alignment if
  • each symbol in the pattern (e.g. A) corresponds to a ungapped column in the alignment where all the characters match the pattern symbol (in the example, A).
  • the wildcards in the pattern are compatible with the number of residues between the corresponding columns in the alignment.

For instance the pattern A-x(2,3)-B is consistent with the alignment




For more details see I. Jonassen
Efficient discovery of conserved patterns using a pattern graph.
Submitted to CABIOS

B Options:
Using the B options (BN,BI,BF) on the menu you can control which pattern symbols will be used during the initial pattern search and during the refinement phase. In the pattern C-x(2)-[DE], C and [DE] are the symbols.

The pattern symbols that can be used, are read from a file if the BI option is set, otherwise a default set will be used.

The default set has as the 20 first elements, the single amino acid symbols, and it also contains a set of ambiguous symbols, each containing amino acids that share some physio-chemical properties

If BI is set, option BF will appear to allow you to give the name of the file. In the file each symbol is given on a separate line contatining the letters that the symbol should match. For instance the file could be:



and only patterns with the symbols C and [DE] would be considered. During the initial search, pattern symbols corresponding to the first BN lines can be used. Increasing BN will slow down the search and increase the memory usage, but allow more ambiguous pattern symbols.

P Options:
The P options are for controlling the patterns to be considered by Pratt. See also the F options for controlling flexibility.
Option PL:
allows you to set the maximum length of a pattern. The length of the pattern C-x(2,4)-[DE] is 1+4+1=6. The memory requirement of Pratt depends on L; a higher L value gives higher memory requirement.
Option PN:
using this you can set the maximum number of symbols in a pattern. The pattern C-x(2,4)-[DE] has 2 symbols (C and [DE]). When PN is increased, Pratt will require more memory.
Option PX:
Using this option you can set the maximum length of a wildcard. Examples of wildcards and lengths are

   x       -  1

  x(10)    - 10

 x(3,4)    -  4

Increasing PX will increase the time used by Pratt, and also slightly the memory required.

F Options:
The F options control flexible wildcards in the patterns:
Option FN:

Using this option you can set the maximum number of flexible wildcards (matching a variable number of arbitrary sequence symbols). For instance x(2,4) is a flexible wildcard, and the pattern


contains one flexible wildcard.

Increasing FN will increase the time used by Pratt.
Option FL:

you can set the maximum flexibility of a flexible wildcard (matching a variable number of arbitrary sequence symbols). For instance x(2,4) and x(10,12) has flexibility 2, and x(10) has flexibility 0. Increasing FL will increase the time used by Pratt.
Option FP:

Using option FP you can set an upper limit on the product of a flexibilities for a pattern. This is related to the memory requirements of the search, and increasing the limit, increases the memory usage. Some patterns and the corresponding product of flexibilities:

C-x(2,4)-[DE]-x(10)-F      - (4-2+1)*(10-10+1)= 3

C-x(2,4)-[DE]-x(10-14)-F   - (4-2+1)*(14-10+1)= 3*5= 15

Option E:
Using the E parameter you can adjust the greediness of the search. Setting E to 0 (zero), the search will be exhaustive. Increasing E increases the greediness, and decreases the time used in the search.

Option R:
When the R option is switched on, patterns found during the initial pattern search are input to a refinement algorithm where more ambiguous pattern symbols can be added.
For instance the pattern


might be refined to


If the RG option is switched on, then ambiguous symbols listed in the symbols file (or in the default symbol set -- see help for option B), are used. If RG is off, only the letters needed to match the input sequences are inlcuded in the ambiguous pattern positions.
For example, if [ILV] is a listed allowed symbol, and [IL] is not, [IL] can be included in a pattern if RG is off, but if RG is on, the full symbol [ILV] will be included instead.

O Options:
The O options allow you to control the output from Pratt:
Option OF:
allows you to specify the name of the file to which Pratt will write its output
Option OP:
when switched on, patterns will be output in PROSITE style (for instance C-x(2,4)-[DE]). When switched off, patterns are output in a simpler consensus pattern style (for instance Cxx--[DE] where x matches exactly one arbitrary sequence symbol and - matches zero or one arbitrary sequence symbol).
Option ON:
set the max. nr of patterns to be found by Pratt.
Option OA:
set the max. nr of patterns for which Pratt is to produce an alignment of the sequence segments matching it.

M Options:
If the M option is set, then Pratt will print out the location of the sequence segments matching each of the (maximum 52) best patterns. The patterns are given labels A, B,...Z,a,b,...z in order of decreasing pattern score. Each sequence is printed on a line, one character per K-tuple in the sequence. If pattern with label C matches the third K-tuple in a sequence C is printed out. If several patterns match in the same K-tuple, only the best will be printed.
Option MR:
sets the K value (ratio) used for printing the summary information about where in each sequence the pattern matches are found.
Option MV:
if set, the output is printed vertically instead of horizontally, vertical output can be better for large sequence sets.

S Options:
The S option allows you to control the scoring of patterns. There are five possible scoring schemes to be used:
patterns are scored by their information content as defined in (Jonassen et al, 1995). Note that a pattern's score is independent of which sequences it matches.
patterns are scored by a Minimum Description Length principle derived scoring scheme, which is related to the one above, but penalises patterns scoring few sequences vs. patterns scoring many. Parameters Z0-Z3 appears when this scoring scheme is used.
a pattern is scored higher if it contains more information and/or if it matches more diverse sequences. The sequence diversity is calculated from a dendrogram which has to be input.
similar to the tree scoring, except a matrix with pairwise the similarity between all pairs of input sequences are used instead of the tree. The matrix has to be input.
- a measure of Positive Predictive Value - it is assumed that the input sequences consitute a family, and are all contained in the Swiss-Prot database. PPV measures how certain one can be that a sequence belongs to the family given that it matches the pattern.
For the last three scoring schemes, an input file is needed and option SF appears allowing the user to set his own file name.

Option X:
Exit the menu, and start the pattern discovery process.

Option Q:
Quit Pratt without searching for patterns.

Help Option:
Help is available on-line from the Pratt's menu. Just type help option for help on a specific option from Pratt's menu.

2.4 Controlling the search via command line options.

All parameters whose values can be set using the menu can also be set from the command line. For parameters with numerical value (for example CM (minimum number of sequences to match a pattern) the value of this parameter is set by including -CM <value> in the command line. If this is the only parameter for which you wish to use a non-default value, your command line might look something like
pratt fasta sequences -cm 20
if you wish to look for patterns matching minimum 20 of the sequences in the file sequences (given in FastA format).

For parameters swithchin on or off options, you should include on or off behind the option on the command line. For example if you do not want pattern refinement to be done, your command line might look like
pratt fasta sequences -cm 20 -r off

Nomally if you set some parameters using the command line, Pratt will just start the search using default values for the parameters that you have not set. If you want to see the menu as well, include -menu in the command line.

First run Pratt using a restrictive set of parameter values (for example the default parameters). If it finds a pattern you're happy with, then you're happy. If not, you can run Pratt again using a less restrictive set of parameters, in one of the following ways:
  1. allow for more ambiguous symbols: Increase B.
  2. allow for longer gaps: Increase W.
  3. allow for more flexibilities: Increase N, F, P.
  4. decrease the minimum number of sequences to match a pattern -- decrease M.

Pratt Homepage.