THE BROAD-HOST-RANGE PLASMID PTF-FC2 REQUIRES A PRIMASE-LIKE PROTEIN FOR AUTONOMOUS REPLICATION IN ESCHERICHIA-COLI

A 3202-bp fragment of plasmid pTF-FC2, cloned into pUC19, had previously been identified as the minimum region required for replication in either Pseudomonas aeruginosa or Escherichia coli polA- mutants. During the course of experiments to construct broad-host-range cloning vectors based on the pTF-FC2 replicon, it was found that the 3202-bp fragment had an absolute requirement for some function of the pUC19 vector. This requirement was eliminated in the presence of co-resident pTF-FC2 derivatives. An additional 1239-bp fragment from pTF-FC2, immediately adjacent to the 3202-bp fragment, was identified which restored the ability of the pTF-FC2 replicon to replicate autonomously. Sequence analysis of the region revealed a single open reading frame encoding a 40-kDa polypeptide, which was synthesised in an in vitro transcription/translation system. A comparison of the amino acid sequence of this protein with sequence data banks revealed limited homology with the RepB' primase of the IncQ plasmid, RSF1010. An M13 DELTA-lac 110 replication-deficient phage system was used to demonstrate that the 40-kDa protein did function as a primase with respect to replication at the origin of replication (vegetative) of pTF-FC2.