Stabilization of the intermediate in frameshift mutation

A mismatch repair, proofreading deficient mutant of Escherichia coli lost a C from a C8 run at a rate 10 times higher than the loss of A from an A8 sequence in the same double mutant. This greater frameshift instability of a homopolymeric run of C's may be due to stabilization of a stacked intermediate. Gain of a (CA) unit in a similarly constructed (CA)15 sequence occurred at a rate about 1/3 that previously reported for a (CA)14 construct losing a (CA) repeat unit.