package org.broadinstitute.sting.utils; import java.util.Random; /** * BaseUtils contains some basic utilities for manipulating nucleotides. */ public class BaseUtils { /// In genetics, a transition is a mutation changing a purine to another purine nucleotide (A <-> G) or // a pyrimidine to another pyrimidine nucleotide (C <-> T). // Approximately two out of every three single nucleotide polymorphisms (SNPs) are transitions. public enum BaseSubstitutionType { TRANSITION, // A <-> G or C <-> T TRANSVERSION } /** * Returns the base substitution type of the 2 state SNP * @param base1 * @param base2 * @return */ public static BaseSubstitutionType SNPSubstitutionType( char base1, char base2 ) { BaseSubstitutionType t = isTransition(base1, base2) ? BaseSubstitutionType.TRANSITION : BaseSubstitutionType.TRANSVERSION; //System.out.printf("SNPSubstitutionType( char %c, char %c ) => %s%n", base1, base2, t); return t; } public static boolean isTransition( char base1, char base2 ) { int b1 = simpleBaseToBaseIndex(base1); int b2 = simpleBaseToBaseIndex(base2); return b1 == 0 && b2 == 2 || b1 == 2 && b2 == 0 || b1 == 1 && b2 == 3 || b1 == 3 && b2 == 1; } public static boolean isTransversion( char base1, char base2 ) { return ! isTransition(base1, base2); } /** Private constructor. No instantiating this class! */ private BaseUtils() {} static public boolean basesAreEqual(byte base1, byte base2) { return simpleBaseToBaseIndex((char)base1) == simpleBaseToBaseIndex((char)base2); } /** * Converts a IUPAC nucleotide code to a pair of bases * * @param code * @return 0, 1, 2, 3, or -1 if the base can't be understood */ static public char[] iupacToBases(char code) { char[] bases = new char[2]; switch (code) { case '*': // the wildcard character counts as an A case 'A': case 'a': bases[0] = bases[1] = 'A'; break; case 'C': case 'c': bases[0] = bases[1] = 'C'; break; case 'G': case 'g': bases[0] = bases[1] = 'G'; break; case 'T': case 't': bases[0] = bases[1] = 'T'; break; case 'R': case 'r': bases[0] = 'A'; bases[1] = 'G'; break; case 'Y': case 'y': bases[0] = 'C'; bases[1] = 'T'; break; case 'S': case 's': bases[0] = 'G'; bases[1] = 'C'; break; case 'W': case 'w': bases[0] = 'A'; bases[1] = 'T'; break; case 'K': case 'k': bases[0] = 'G'; bases[1] = 'T'; break; case 'M': case 'm': bases[0] = 'A'; bases[1] = 'C'; break; default: bases[0] = bases[1] = 'N'; } return bases; } /** * Converts a simple base to a base index * * @param base [AaCcGgTt] * @return 0, 1, 2, 3, or -1 if the base can't be understood */ static public int simpleBaseToBaseIndex(char base) { switch (base) { case '*': // the wildcard character counts as an A case 'A': case 'a': return 0; case 'C': case 'c': return 1; case 'G': case 'g': return 2; case 'T': case 't': return 3; default: return -1; } } /** * Converts a base index to a simple base * * @param baseIndex 0, 1, 2, 3 * @return A, C, G, T, or '.' if the index can't be understood */ static public char baseIndexToSimpleBase(int baseIndex) { switch (baseIndex) { case 0: return 'A'; case 1: return 'C'; case 2: return 'G'; case 3: return 'T'; default: return '.'; } } /** * Converts a base index to a base index representing its cross-talk partner * * @param baseIndex 0, 1, 2, 3 * @return 1, 0, 3, 2, or -1 if the index can't be understood */ static public int crossTalkPartnerIndex(int baseIndex) { switch (baseIndex) { case 0: return 1; // A -> C case 1: return 0; // C -> A case 2: return 3; // G -> T case 3: return 2; // T -> G default: return -1; } } /** * Converts a base to the base representing its cross-talk partner * * @param base [AaCcGgTt] * @return C, A, T, G, or '.' if the base can't be understood */ static public char crossTalkPartnerBase(char base) { return baseIndexToSimpleBase(crossTalkPartnerIndex(simpleBaseToBaseIndex(base))); } /** * Return the complement of a base index. * * @param baseIndex the base index (0:A, 1:C, 2:G, 3:T) * @return the complementary base index */ static public byte complementIndex(int baseIndex) { switch (baseIndex) { case 0: return 3; // a -> t case 1: return 2; // c -> g case 2: return 1; // g -> c case 3: return 0; // t -> a default: return -1; // wtf? } } /** * Return the complement of a base, or the specified base if it can't be complemented (i.e. an ambiguous base). * * @param base the base [AaCcGgTt] * @return the complementary base, or the input base if it's not one of the understood ones */ static public byte simpleComplement(char base) { switch (base) { case 'A': case 'a': return 'T'; case 'C': case 'c': return 'G'; case 'G': case 'g': return 'C'; case 'T': case 't': return 'A'; default: return (byte) base; } } /** * Reverse complement a byte array of bases (that is, chars casted to bytes, *not* base indices in byte form) * * @param bases the byte array of bases * @return the reverse complement of the base byte array */ static public byte[] simpleReverseComplement(byte[] bases) { byte[] rcbases = new byte[bases.length]; for (int i = 0; i < bases.length; i++) { rcbases[i] = simpleComplement((char) bases[bases.length - 1 - i]); } return rcbases; } /** * Reverse complement a String of bases. Preserves ambiguous bases. * * @param bases the String of bases * @return the reverse complement of the String */ static public String simpleReverseComplement(String bases) { return new String(simpleReverseComplement(bases.getBytes())); } /** * Reverse a byte array of bases * * @param bases the byte array of bases * @return the reverse of the base byte array */ static public byte[] reverse(byte[] bases) { byte[] rcbases = new byte[bases.length]; for (int i = 0; i < bases.length; i++) { rcbases[i] = bases[bases.length - i - 1]; } return rcbases; } /** * For the most frequent base in the sequence, return the percentage of the read it constitutes. * * @param sequence the read sequence * @return the percentage of the read that's made up of the most frequent base */ static public double mostFrequentBaseFraction(byte[] sequence) { int[] baseCounts = new int[4]; for ( byte base : sequence ) { int baseIndex = simpleBaseToBaseIndex((char) base); if (baseIndex >= 0) { baseCounts[baseIndex]++; } } int mostFrequentBaseIndex = 0; for (int baseIndex = 1; baseIndex < 4; baseIndex++) { if (baseCounts[baseIndex] > baseCounts[mostFrequentBaseIndex]) { mostFrequentBaseIndex = baseIndex; } } return ((double) baseCounts[mostFrequentBaseIndex])/((double) sequence.length); } /** * Return a random base index (A=0, C=1, G=2, T=3). * * @return a random base index (A=0, C=1, G=2, T=3) */ static public int getRandomBaseIndex() { return getRandomBaseIndex(-1); } /** * Return a random base index, excluding some base index. * * @param excludeBaseIndex the base index to exclude * @return a random base index, excluding the one specified (A=0, C=1, G=2, T=3) */ static public int getRandomBaseIndex(int excludeBaseIndex) { int randomBaseIndex = excludeBaseIndex; Random generator = new Random(); while (randomBaseIndex == excludeBaseIndex) { randomBaseIndex = generator.nextInt(4); } return randomBaseIndex; } /** * Return a random base (A, C, G, T). * * @return a random base (A, C, G, T) */ static public char getRandomBase() { return getRandomBase('.'); } /** * Return a random base, excluding some base. * * @param excludeBase the base to exclude * @return a random base, excluding the one specified (A, C, G, T) */ static public char getRandomBase(char excludeBase) { return BaseUtils.baseIndexToSimpleBase(getRandomBaseIndex(BaseUtils.simpleBaseToBaseIndex(excludeBase))); } /** Computes the smallest period >= minPeriod for the specified string. The period is defined as such p, * that for all i = 0... seq.length-1, seq[ i % p ] = seq[i] (or equivalently seq[i] = seq[i+p] for i=0...seq.length-1-p). * The sequence does not have to contain whole number of periods. For instance, "ACACACAC" has a period * of 2 (it has a period of 4 as well), and so does * "ACACA"; similarly, smallest periods of "CTCCTC", "CTCCT", and "CTCC" are all equal to 3. The "trivial" period is * the length of the string itself, and it will always be returned if no smaller period can be found in the specified period range * or if specified minPeriod is greater than the sequence length. * * @param seq * @return */ public static int sequencePeriod(String seq, int minPeriod) { int period = ( minPeriod > seq.length() ? seq.length() : minPeriod ); // we assume that bases [0,period-1] repeat themselves and check this assumption // until we find correct period for ( int pos = period ; pos < seq.length() ; pos++ ) { int offset = pos % period; // we are currenlty 'offset' bases into the putative repeat of period 'period' // if our current hypothesis holds, base[pos] must be the same as base[offset] if ( Character.toUpperCase( seq.charAt(pos) ) != Character.toUpperCase( seq.charAt( offset ) ) ) { // period we have been trying so far does not work. // two possibilities: // A) offset = 0, i.e. current position pos must be start of the next repeat, but it is not; // in this case only bases from start up to the current one, inclusive, may form a repeat, if at all; // so period is at least pos+1 (remember, pos is 0-based), then on the next loop re-entrance // pos will be autoincremented and we will be checking next base // B) offset != 0, i.e. the current base breaks the repeat, but maybe it starts a new one? // hence we should first check if it matches the first base of the sequence, and to do that // we set period to pos (thus trying the hypothesis that bases from start up to the current one, // non-inclusive are repeated hereafter), and decrement pos (this will re-test current base against the first base // on the next loop re-entrance after pos is autoincremented) if ( offset == 0 ) period = pos+1; else period = pos-- ; } } return period; } } /* code snippet for testing sequencePeriod(): * * String str = "CCTTG"; int p = 0; System.out.print("Periods of " + str +" are:"); while ( p < str.length() ) { p = sequencePeriod(str, p+1); System.out.print(" "+p); } System.out.println(); System.exit(1); */