bioinformatic phd. course

Bioinformatic PhD. course

Bioinformatics

Xavier Messeguer Peypoch (http://www.lsi.upc.es/~alggen)

LSI Dep. de Llenguatges i Sistemes InformàticsBSC Barcelona Supercomputing Center

Universitat Politècnica de Catalunya

Contents

1. Biological introduction

Exact Extended Approximate

6. Projects: PROMO, MREPATT, …

5. Sequence assembly

2. Comparison of short sequences ( up to 10.000bps)

Dot Matrix Pairwise align. Multiple align. Hash alg.

3. Comparison of large sequences ( more that 10.000bps)

Data structures Suffix trees MUMs

4. String matching

String matching

1. (Exact) String matching of one pattern

2. (Exact) String matching of many patterns

3. Extended string matching

3. Approximate string matching (Dynamic programming)

• Flexible pattern matching in stringsG. Navarro and M. Raffinot, 2002, Cambridge Uni. Press

• Algorithms on strings, trees and sequencesD. Gusfield, Cambridge University Press, 1997

String matching

Definition: given a long text T and a set of k patterns p1,p2,…,pk, the string matching problem is to find

all the ocurrences of all the patterns in the text T.

On-line algorithms: the patterns are known.

Off-line algorithms: the text is known.

• Only one pattern (exact and approximated)• Five, ten, hundred, thusand,.. patterns (exact)

• Suffix trees

Master Course

First part:

(Exact) string matching

String matching: one pattern

For instance, given the sequence

CTACTACTACGTCTATACTGATCGTAGCTACTACATGC

search for the pattern ACTGA.

How does the string algorithms made the search?

and for the pattern TACTACGGTATGACTAA

String Matching: Brute force algorithm

Given the pattern ATGTA, the search is

G T A C T A G A G G A C G T A T G T A C T G ...A T G T A

A T G T A

Example:

Connect to

http://www-igm.univ-mlv.fr/~lecroq/string/index.html

and open Brute Force algorithm

String Matching of one pattern

The cost of Brute Force algorithm is O(nm),

Can the search be made with lower cost?

TACTACGGTATGACTAA

Factor search

Prefix search

Suffix search

and the expected number of comparisons?

String matching of one pattern

How does the string algorithms made the search?

There is a sliding window along the text against which the pattern is compared:

Pattern :

Text :

Which are the facts that differentiate the algorithms?

1. How the comparison is made.2. The length of the shift.

At each step the comparison is made and the window is shifted to the right.

Text :

Pattern :

From left to right: prefix search

• Which is the next position of the window?

• How the comparison is made?

Pattern :

Text :

The window is shifted only one cell

The cost is O(mn).

String Matching: one pattern

Most efficient algorithms (Navarro & Raffinot)

2 4 8 16 32 64 128 256

Length of the pattern

Horspool

BNDMBOM

BNDM : Backward Nondeterministic Dawg Matching

BOM : Backward Oracle Matching

String Matching: Horspool algorithm

Text :

Pattern :From right to left: suffix search

• Which is the next position of the window?

Pattern :

Text : a

It depends of where appears the last letter of the text, say it ‘a’, in the pattern:

Then it is necessary a preprocess that determines the length of the shift.

Given the pattern ATGTA, the shift table is A 4C 5G 2T 1

And the search: G T A C T A G A G G A C G T A T G T A C T G ...A T G T A

A T G T A

A T G T A A T G T A

A T G T A

Example:

Given the pattern ATGTA, the shift table is A 4C 5G 2T 1

And the search: G T A C T A G A G G A C G T A T G T A C T G ...A T G T A

A T G T A

A T G T A A T G T A

Example:

…http://www-igm.univ-mlv.fr/~lecroq/string/index.html

The most efficient algorithms (Navarro & Raffinot)

2 4 8 16 32 64 128 256

Horspool

BNDMBOM

What happens with many patterns?

String matching: many patterns

Given the sequence

Search for the patterns

ACTGACTGTCTAATT

ACTGATCTTTGTAGCAATACTACATGCACTGA.

Horspool for many patterns

Search for ATGTATG,TATG,ATAAT,ATGTG

4. Start the search

1. Build the trie of the inverted patterns

2. lmin=4A 1C 4 (lmin)G 2T 1

3. Table of shifts

The text ACATGCTATGTGACA…

A 1C 4 (lmin)G 2T 1

Short Shifts!

AA 1 AC 3 (LMIN-L+1)AG 3AT 1CA 3CC 3CG 3…

2 símbols

Horspool to Wu-Manber

How do we can increase the length of the shifts?

With a table shift of l-mers with the patterns ATGTATG,TATG,ATAAT,ATGTG

AA 1AT 1GT 1TA 2TG 2

A 1C 4 (lmin)G 2T 1

1 símbol

Wu-Manber algorithm

into the text: ACATGCTATGTGACATAATA

AA 1AT 1GT 1TA 2TG 2

Experimental length: log|Σ| 2*lmin*r

String matching of many patterns

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOMLmin

(5 patterns)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM(10 patterns)

5 10 15 20 25 30 35 40 45

Wu-Manber

(100 patterns)

2 4 8 16 32 64 128 256

Horspool

BNDMBOM

BNDM algorithm

• How the shift is determined?

Text :

Pattern :

Searches for suffixes of T that are factors of P

This state is expressed with an array D of bits:

D2 = 1 0 0 0 1 0 0

How the next state can be obtained?

D = D<<1 & B(x)

Given the mask B(x) of x, the cells where character x appears into the pattern

D3 = (0 0 0 1 0 0 0) & (0 0 1 1 0 0 0 ) = (0 0 0 1 0 0 0 )

If B(x) = ( 0 0 1 1 0 0 0) then

BNDM algorithm: example

Given the pattern ATGTA,

the mask of characters is:

B(A) = ( 1 0 0 0 1 )B(C) = B(G) = B(T) =

B(A) = ( 1 0 0 0 1 )B(C) = ( 0 0 0 0 0 )B(G) = ( 0 0 1 0 0 )B(T) = ( 0 1 0 1 0 )

Given the text :G T A C T A G A G G A C G T A T G T A C T G ...A T G T A

A T G T A

B(A) = ( 1 0 0 0 1 )B(C) = ( 0 0 0 0 0 )B(G) = ( 0 0 1 0 0 )B(T) = ( 0 1 0 1 0 )

D1 = ( 0 1 0 1 0 )D2 = ( 1 0 1 0 0 ) & ( 0 0 0 0 0 ) = ( 0 0 0 0 0 )

D1 = ( 0 0 1 0 0 )D2 = ( 0 1 0 0 0 ) & ( 0 0 1 0 0 ) = ( 0 0 0 0 0 )

D1 = ( 1 0 0 0 1 )D2 = ( 0 0 0 1 0 ) & ( 0 1 0 1 0 ) = ( 0 0 0 1 0 )D3 = ( 0 0 1 0 0 ) & ( 0 0 1 0 0) = ( 0 0 1 0 0 )D4 = ( 0 1 0 0 0 ) & ( 0 0 0 0 0) = ( 0 0 0 0 0 )

A T G T A

The pattern is ATGTA ,

the masks are:

and the text:G T A C T A G A G G A C G T A T G T A C T G ...A T G T A

B(A) = ( 1 0 0 0 1 )B(C) = ( 0 0 0 0 0 )B(G) = ( 0 0 1 0 0 )B(T) = ( 0 1 0 1 0 )

D1 = ( 1 0 0 0 1 )D2 = ( 0 0 0 1 0 ) & ( 0 1 0 1 0 ) = ( 0 0 0 1 0 )D3 = ( 0 0 1 0 0 ) & ( 0 0 1 0 0 ) = ( 0 0 1 0 0 )D4 = ( 0 1 0 0 0 ) & ( 0 1 0 1 0 ) = ( 0 1 0 0 0 )D5 = ( 1 0 0 0 0 ) & ( 1 0 0 0 1 ) = ( 1 0 0 0 0 )D6 = ( 0 0 0 0 0 ) & ( * * * * * ) = ( 0 0 0 0 0 )

Pattern found!

Text :

Pattern :

BNDM algorithm

D = 1 0 0 0 1 0 0

Text :

Pattern :

BNDM algorithm

D = 1 0 0 0 1 0 0

If the left bit is set to one in step i, it means that a prefix of P of length i is equal to a suffix of T, then the window is shifted m-i cells; otherwise it is shifted m cells

String matching: one pattern

2 4 8 16 32 64 128 256

Long. patró

Horspool

BNDMBOM

BOM (Backward Oracle Matching)

• How the shifted is determined?

Text :

Pattern : Automaton: Factor Oracle(1999)

Checks if the suffix is a factor of the pattern

Automaton Factor Oracle: properties

Factor Oracle of the word G T A T G T A

GG AT T ATTA

G T A T G

but the automaton also recognizes other strings as G T G

then it is usefull only for discard words out as factors!

T A T G

Suffixes found before.

Suffixes that have not been found before.

BOM: example

• The Factor Oracle of the inverted pattern is built. Given the pattern ATGTATG

• Search: G T A C T A G A A T G T G T A G A C A T G T A T G G T G A...A T G T A T G

GG AT T ATTA

BOM: example

• Search: G T A C T A G A A T G T G T A G A C A T G T A T G G T GA T G T A T G

GG AT T ATTA

A T G T A T G

BOM: example

• Search G T A C T A G A A T G T G T A G A C A T G T A T G G T G A T G T A T G

GG AT T ATTA

A T G T A T G A T G T A T G

BOM: example

• Search : G T A C T A G A A T G T G T A G A C A T G T A T G G T GA T G T A T G

GG AT T ATTA

A T G T A T G

BOM: example

• Search : G T A C T A G A A T G T G T A G A C A T G T A T G G T G ...A T G T A T G

GG AT T ATTA

BOM: example

• Es construeix l’autòmata del patró invers: Suposem que el patró és ATGTATG

• Search : G T A C T A G A A T G T G T A G A C A T G T A T G G T G ...A T G T A T G

GG AT T ATTA

A T G T A T G …

BOM (Backward Oracle Matching)

Text :

Pattern : Automaton: Factor Oracle

Checks if the suffix is a factor of the pattern

• a is the first mismatch

But what happens with many patterns?

Text :

Pattern : Automaton: Factor Oracle

Checks if the suffix is a factor of any pattern

Factor Oracle of many patterns

The AFO of GTATGTA, GTAA, TAATA i GTGTA

GG AT TT

SBOM algorithm

Text :

Patrons:

Autòmaton………… of lenght lmin

• If the a doesn’t appears in the AFO

• If lmin characters have been read

SBOM algorithm : example

Search for the patterns ATGTATG, TAATG,TAATAAT i AATGTG

GG AT TTTA

ACATGCTAGCTATAATAATGTATG

SBOM algorithm: example

GG AT TTTA

ACATGCTAGCTATAATAATGT…

Alg. Cerca exacta de molts patrons

5 10 15 20 25 30 35 40 45

| |Wu-Manber

SBOMLong. mínima

(5 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM(10 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM (1000 mots)

5 10 15 20 25 30 35 40 45

Wu-ManberSBOM

(100 mots)

PhD. Course

Second part:

Extended string matching

There are characters in the text that represent sets of simbols

1. Classes of characters in the text.

There are characters in the pattern that represent sets of simbols

2. Classes of characters in the pattern.

There are classes of characters represented by oneSymbol. For instace the IUPAC code for the

DNA alphabet is:R = {G,A} Y = {T,C} K = {G,T} M = {A,C} S = {G,C} W = {A,T}

B = {G,T,C } D = {G,A,T} H = {A,C,T} V = {G,C,A} N = {A,G,C,T} (any)

Classes in the text

Algorismes més eficients (Navarro & Raffinot)

2 4 8 16 32 64 128 256

Long. patró

Horspool

BNDMBOM

Alg. Cerca exacta d’un patró (text on-line)

2 4 8 16 32 64 128 256

Long. patró

Horspool

BNDMBOM

Classes in the text :Horspool example

Given the pattern ATGTA

• the shift table is:

A 4C 5G 2T 1R ?…N ?

A 4C 5G 2T 1R 2…N ?

A 4C 5G 2T 1R 2…N 1

Given the text : G T A R T R N A A G G A …A T G T A

A T G T A

• and the shift table:

A 4C 5G 2T 1R 2…N 1

Given the text : G T A R T R N A A G G A ...A T G T A

A T G T A

A T G T A A T G T A

Alg. Cerca exacta d’un patró (text on-line)

2 4 8 16 32 64 128 256

Long. patró

Horspool

BNDMBOM

Classes in the text: BOM

• Com es determina la següent posició de la finestra?

• Com fa la comparació?

Text :

Patró : Autòmata: Factor Oracle

Comproba si el sufix és factor del patró

Però primer analitzem com fa la comparació…

Classes in the text: BOM example

• Es construeix l’autòmata del patró invers: Suposem que el patró és ATGTATG

• I la cerca sobre el text : G T A R T R N A A T G…A T G T A T G

• Com fa la comparació?

GG AT T ATTA

No és possible cap millora!

5 10 15 20 25 30 35 40 45

| |Wu-Manber

SBOMLong. mínima

(5 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM(10 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM (1000 mots)

5 10 15 20 25 30 35 40 45

Wu-ManberSBOM

(100 mots)

5 10 15 20 25 30 35 40 45

| |Wu-Manber

SBOMLong. mínima

(5 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM(10 mots)

5 10 15 20 25 30 35 40 45

Wu-Manber

SBOM (1000 mots)

5 10 15 20 25 30 35 40 45

Wu-ManberSBOM

(100 mots)

Classes in the text: Set Horspool

Search for the patterns ATGTATG,TATG,ATAAT,ATGTG

In the text: ARTGNCTATGTGACA…

it’s not possible any improvment!

Master Course

Third part:

Regular expressions matching

Expressions regulars

Una expressió regular ℛ és una cadena sobre Σ U { ε, |, · , * , (, ) } definida recursivament com:

• ε és una expressió regular• Un caràcter de Σ és una expressió regular

• ( ) ℛ és una expressió regular

• ℛ1 · ℛ2 és una expressió regular

• ℛ * és una expressió regular

• ℛ1 | ℛ2 és una expressió regular

Llenguatge regular

El llenguatge representat per una expressió regular és el conjunt dels mots que es poden construir a partir

de l’expressió regular.

El problema de buscar una expressió regular dins el text és el de buscar tots els factors que pertanyen

al respectiu llenguatge regular.

Cerca d’una expressió regular

expressió regular

Cerca de les ocurrències

Cerca amb autòmat determinista

Cerca amb el bit-paral.lel Thompson

arbre “parser”

PhD. Course

Fourth part:

Approximate string matching

For instance, given the sequence

search for the pattern ACTGA allowing one error…

… but what is the meaning of “one error”?

Edit distance

We accept three types of errors:

The edit distance d between two strings is the minimum number of

substitutions,insertions and deletionsneeded to transform the first string into the second one

d(ACT,ACT)= d(ACT,AC)= d(ACT,C)=d(ACT,)= d(AC,ATC)= d(ACTTG,ATCTG)=

3. Deletion: ACCGTGAT ACCGGAT

2. Insertion: ACCGTGAT ACCGATGAT

1. Mismatch: ACCGTGAT ACCGAGAT

Edit distance

d(ACT,ACT)=0 d(ACT,AC)=1 d(ACT,C)=2d(ACT,)= d(AC,ATC)= d(ACTTG,ATCTG)=

Edit distance

d(ACT,ACT)=0 d(ACT,AC)=1 d(ACT,C)=2d(ACT,)= 3 d(AC,ATC)=1 d(ACTTG,ATCTG)=2

Edit distance

• ACT and ACT : ACT ACT

• ACTTG and ATCTG:

• ACT and AC: ACT AC-

ACTTG ATCTG

ACT - TGA - TCTG

Given d(ACT,ACT)=0 d(ACT,AC)=1 d(ACTTG,ATCTG)=2which is the best alignment in every case?

The Edit distance is related with the best alignment of strings

Edit distance

But which is the distance between the strings

ACGCTATGCTATACG and ACGGTAGTGACGC?

… and the best alignment between them?

1966 was the first time this problem was discussed…

and the algorithm was proposed in 1968,1970,…

using the technique called “Dynamic programming”

Edit distance

C T A C T A C T A C G T ACTGA

The cell contains the distance between AC and CTACT.

Edit distance and alignment of strings

C T A C T A C T A C G T A C T GA

C T A C T A C T A C G T 0 A C T GA

C T A C T A C T A C G T 0 1 A C T GA

C T A C T A C T A C G T 0 1 2 A C T GA

C T A C T A C T A C G T 0 1 2 3 4 5 6 7 8 …A C T GA

- - - - - -CTACTA

C T A C T A C T A C G T 0 1 2 3 4 5 6 7 8 …A ?C ?T ?GA

C T A C T A C T A C G T 0 1 2 3 4 5 6 7 8 …A 1C 2T 3G…A

ACT - - -

Connect to

http://alggen.lsi.upc.es/docencia/ember/leed/Tfc1.htm

and use the global method.

K-approximate string searching

How this algorithm can be applied

to the approximate search?

to the K-approximate string searching?

C T A C T A C T A C G T A C T G G T G A A …

This cell …

This cell gives the distance between (ACTGA, CT…GTA)…

…but we only are interested in the last characters

* * * * * * C T A C G T A C T G G T G A A …

…but we only are interested in the last characters…

…no matter where they appears in the text, then…

* * * * * * C T A C G T A C T G G T G A A … 0ACTGA

C T A C T A C T A C G T A C T G G T G A A … 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0ACTGA

…no matter where they appears in the text, then

Connect to

http://alggen.lsi.upc.es/docencia/ember/leed/Tfc1.htm

and use the semi-global method.

bioinformatic phd. course

extended string matching

string matching definition

string matching problem

string algorithms

approximate string

string matchingstring

pattern atgta

pattern actga

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