PCNB IS REQUIRED FOR THE RAPID DEGRADATION OF RNAI, THE ANTISENSE RNATHAT CONTROLS THE COPY NUMBER OF COLE1-RELATED PLASMIDS

The replication of ColE1-related plasmids is controlled by an unstable antisense RNA, RNAI, which can interfere with the successful processi ng of the RNAII primer of replication. We show here that a host protei n, PcnB, supports replication by promoting the decay of RNAI. In bacte rial strains deleted for pcnB a stable, active form of RNAI, RNAI, wh ich appears to be identical to the product of 5'-end processing by RNA se E, accumulates. This leads to a reduction in plasmid copy number. W e show, using a GST-PcnB fusion protein, that PcnB does not interfere with RNAI/RNAII binding in vitro. The fusion protein, like PcnB, has p olyadenylating activity and is able to polyadenylate RNAI (and also an other antisense RNA, CopA) in vitro.