Neither absence nor excess of λ O initiator‐digesting ClpXP protease affects λ plasmid or phage replication in Escherichia coli

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Abstract
Owing to rapid proteolysis of the coliphage λ-coded initiator protein, λ O, this protein is considered to carry a rate–limiting step in λ DNA replication. The discovery of ClpXP protease responsible for λ O protein turnover allowed an opportunity to verify this hypothesis. However, neither absence nor excess of this protease significantly affected the transformation efficiency and copy number of λ plasmid, or the Kinetics of the λ phage growth. These results are also incompatible with the hypothesis that the stabilization of λ O plays a role in the switch from early (circle-to-circle) to late (rolling-circle) λ phage DNA replication. Tran-scriptional activation of oriλ probably assisted by the Escherichia coli DnaA function, remains as the possible rate-limiting step in λ DNA replication.