Transcription initiation of the copy-number control and better-thanrandom segregation genes of the broad-host-range and low-copynumber plasmid pSM19035 are subjected to repression by the autoregulated pSM19035-encoded product in Bacillus subtilis cells. The promoters of the copS (Pcop1 and Pcop2), ␦ (P␦), and (P) genes have been mapped. These promoters are embedded in a set of either seven copies of a 7-bp direct repeat or in a block consisting of two 7-bp direct repeats and one 7-bp inverted repeat; the blocks are present either two or three times. The cooperative binding of protein to the repeats on the Pcop1, Pcop2, P␦, and P promoters represses transcription initiation by a mechanism that does not exclude A RNAP from the promoters. These results indicate that protein regulates plasmid maintenance by controlling the copy number on the one hand and by regulating the amount of proteins required for better-than-random segregation on the other hand.plasmid replication ͉ Gram-positive bacteria ͉ protein-DNA interactions ͉ transcriptional repressor

Bacillus subtilis RecU protein is involved in homologous recombination, DNA repair, and chromosome segregation. Purified RecU binds preferentially to three- and four-strand junctions when compared to single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) (≈10- and ≈40-fold lower efficiency, respectively). RecU cleaves mobile four-way junctions but fails to cleave a linear dsDNA with a putative cognate site, a finding consistent with a similar genetic defect observed for genes classified within the ε epistatic group (namely ruv A, rec D, and rec U). In the presence of Mg 2+ , RecU also anneals a circular ssDNA and a homologous linear dsDNA with a ssDNA tail and a linear ssDNA and a homologous supercoiled dsDNA substrate. These results suggest that RecU, which cleaves recombination intermediates with high specificity, might also help in their assembly.