REPLICATION STRAND PREFERENCE FOR DELETIONS ASSOCIATED WITH DNA PALINDROMES

We have isolated and sequenced a set of deletions stimulated by DNA pa lindromes in Escherichia coli. All of the deletions are asymmetric wit h respect to the parental sequence and have occurred at short direct r epeats. This is consistent with deletion by strand slippage during DNA replication. The orientation of the asymmetry in such deletion produc ts is diagnostic of the direction of the strand slippage event. It is therefore also diagnostic of its occurrence on the leading or lagging strand of the replication fork when the direction of replication is kn own. In all cases in which the orientation of the asymmetry could be d etermined with respect to DNA replication, the products were consisten t with a preference for deletion on the lagging strand of the fork. Th e data include replication slippage in three situations: on the chromo some of E. coli, in bacteriophage lambda and in high-copy-number pUC-b ased plasmids.