EXPANSION OF CTG REPEATS FROM HUMAN-DISEASE GENESIS DEPENDENT UPON REPLICATION MECHANISMS IN ESCHERICHIA-COLI - THE EFFECT OF LONG PATCH MISMATCH REPAIR REVISITED

Many human hereditary disease genes have been recently associated with the expansion of CTG/GAC repeats. We have used a plasmid-based assay in Escherichia coli to investigate the instability of a (CTG/GAC) inse rt containing 64 repeats. Using this assay, expansions were biochemica lly detected and subsequently quantified. We show that the occurence o f expansions within these trinucleotide repeats is dependent upon repl icative mechanisms. Expansions of up to 30 repeats and deletions of al most all possible sizes occurred regardless of the orientation of the insert relative to the replication origin. In contradiction to a previ ous report, the mismatch repair pathway was found to strongly stabiliz e these repeat stretches. (C) 1998 Academic Press.