NON-WATSON-CRICK BASE-PAIRS MODULATE HOMOLOGOUS ALIGNMENTS IN RECA PAIRING REACTIONS

Complementary pairing by RecA vc;as examined in vitro to investigate h ow homology is deciphered from non-homology. Somewhere in a window of 40-50% sequence complementarity, RecA pairing begins to manifest the s pecificity of homology. Quantitation reveals a hierarchy among non-Wat son-Crick; mispairs: RecA reaction treats sis out of 12 possible mispa irs as good ones and three each of the remaining ones as moderate and bad pairs, The mispairs seem to function as independent pairing units free of sequence context effects, The overall strength of pairing is s imply the sum of the constituent units, RecA mediated gradation of mis pairs, free of sequence contest effects, might offer a general thumb-r ule for predicting the pairing strength of any alignment that carries multiple mispairs. (C) 1998 Federation of European Biochemical Societi es.