Plasmid copy-number control and better-than-random segregation genes of pSM19035 share a common regulator

Transcription initiation of the copy-number control and better-than-random segregation genes of the broad-host-range and low-copy-number plasmid pSM19 035 are subjected to repression by the autoregulated pSM19035-encoded omega product in Bacillus subtilis cells. The promoters of the cops (Pcop1 and P cop2), delta (P delta), and omega (P omega) genes have been mapped. These p romoters are embedded in a set of either seven copies of a 7-bp direct repe at or in a block consisting of two 7-bp direct repeats and one 7-bp inverte d repeat; the blocks are present either two or three times. The cooperative binding of omega protein to the repeats on the Pcop1, Pcop2, P delta, and P omega promoters represses transcription initiation by a mechanism that do es not exclude sigma(A)RNAP from the promoters. These results indicate that omega protein regulates plasmid maintenance by controlling the copy number on the one hand and by regulating the amount of proteins required for bett er-than-random segregation on the other hand.