Stability of reiterated sequences in the Bacillus subtilis chromosome

The instability of reiterated sequences in the Bacillus subtilis chromosome that was previously reported (M. Young, J. Gen. Microbiol. 130:1613-1621, 1984) results from the presence of a truncated pC194 replication origin together with an intact replication protein A gene in the amplified DNA. Removal of the truncated pC194 replication origin or inactivation of replication protein A stabilizes reiterated sequences, whereas provision of replication protein A in trans destabilizes them. We suggest that residual activity of protein A at the truncated replication origin generates single-stranded DNA, which stimulates recombination between repeated sequences and thus destabilizes amplified structures.