The Interaction Of Omega(2) With The Rna Polymerase Beta ' Subunit Functions As An Activation To Repression Switch

The omega gene is encoded in broad-host range and low-copy plasmids. It is genetically linked to antibiotic resistance genes of the major human pathogens of phylum Firmicutes. The homodimeric forms of omega (omega(2)) coordinate the plasmid copy number control, faithful partition (omega(2) and delta(2)) and better-than-random segregation (zeta epsilon(2)zeta) systems. The promoter (P) of the omega epsilon zeta operon (P-omega) transiently interacts with omega(2). Adding delta(2) facilitates the formation of stable omega(2)center dot P-omega complexes. Here we show that limiting omega(2) interacts with the N-terminal domain of the beta' subunit of the Bacillus sub-tilis RNA polymerase (RNAP-sigma(A)) vegetative holoenzyme. In this way omega(2) recruits RNAP-sigma(A) onto P-omega DNA. Partial P-omega occupancy by omega(2) increases the rate at which RNAP-sigma(A) complex shifts from its closed (RPC) to open (RPO) form. This shift increases transcription activation. Adding delta(2) further increases the rate of P-omega transcription initiation, perhaps by stabilizing the omega(2)center dot P-omega complex. In contrast, full operator occupancy by omega(2) facilitates RPC formation, but it blocks RPO isomerization and represses P-omega utilization. The stimulation and inhibition of RPO formation is the mechanism whereby omega(2) mediates copy number fluctuation and stable plasmid segregation. By this mechanism, omega(2) also indirectly influences the acquisition of antibiotic resistance genes.