NEITHER ABSENCE NOR EXCESS OF LAMBDA-O-INITIATOR-DIGESTING CLPXP PROTEASE AFFECTS LAMBDA-PLASMID OR PHAGE REPLICATION IN ESCHERICHIA-COLI

Owing to rapid proteolysis of the coliphage lambda-coded initiator pro tein, lambda O, this protein is considered to carry a rate-limiting st ep in lambda DNA replication. The discovery of ClpXP protease responsi ble for lambda O protein turnover allowed an opportunity to verify thi s hypothesis. However, neither absence nor excess of this protease sig nificantly affected the transformation efficiency and copy number of l ambda plasmid, or the kinetics of the lambda phage growth. These resul ts are also incompatible with the hypothesis that the stabilization of lambda O plays a role in the switch from early (circle-to-circle) to late (rolling-circle) lambda phage DNA replication. Transcriptional ac tivation of ori lambda, probably assisted by the Escherichia coil DnaA function, remains as the possible rate-limiting step in lambda DNA re plication.