Plasmid RP4 encodes two forms of a DNA primase

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The broad host range plasmid RP4 is crucial for bacterial conjugation.
• DNA primase is essential for DNA replication initiation.

Purpose of the Study:

• To investigate the gene locus encoding DNA primase on the RP4 plasmid.
• To elucidate the origin and function of the two primase forms.

Main Methods:

• Deletion analysis using Pri+-recombinant plasmids.
• Analysis of primase polypeptide products.
• Complementation assays with Escherichia coli dnaG3 (ts) mutant.

Main Results:

• The RP4 plasmid's pri gene locus encodes two related DNA primase forms (118 and 80 kDa).
• These primase forms are distinct translation products from an in-phase overlapping gene.
• RP4 mutant primase can functionally substitute for E. coli primase in vivo.

Conclusions:

• The pri gene locus on RP4 exhibits an overlapping gene arrangement producing two primase polypeptides.
• RP4 DNA primase is functionally conserved and can complement E. coli primase deficiency.