Plasmid DNA Primases and their Role in Bacterial Conjugation
RNA primers necessary for starting DNA chain growth are generally made by the transcriptional activity of a group of enzymes called DNA primases. The primase of Escherichia coli is the 60,000 dalton (60 kd) product of the dnaG gene, which functions to generate primers for discontinuous replication of the bacterial chromosome and of at least some plasmids, as well as for complementary strand- synthesis on certain single-stranded genomes (24). Recently a variety of conjugative plasmids have been shown to encode DNA primases active in an assay requiring primer synthesis on single-stranded phage fd DNA. The list includes members of the B, C, I1. (= Iα), I1+B, I2, K, M, P, and U incompatibility groups (44). Representative plasmids of most of the other groups, including F, have been screened in this assay and are currently classified as primase negative (26), but it is possible that some may specify DNA primases that are unable to use fd DNA as a template. In this article, which concentrates on the primases specified by ColIb-P9 (IncI1), RP4 (IncP), and R16 (IncB), we review the biochemistry of these enzymes and the organization of the appropriate structural genes, and discuss the physiological role of their products in plasmid DNA metabolism during bacterial conjugation.
KeywordsDonor Cell Recipient Cell Conjugative Plasmid Bacterial Conjugation dnaC Protein
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