The nucleotide sequence of the DNA encoding the traM, finP and the promoter proximal segment of the traJ gene of the F plasmid has been determined. The predicted amino acid sequence for the traM protein shows that this inner membrane protein contains no signal sequence. The promoters for both the traM and traJ genes have been mapped by in vitro transcription and nuclease S1 protection experiments. No unambiguous location can be assigned to the finP gene but all candidates, if translated, would encode small proteins of between 24 and 52 amino acids.

The DNA sequence of the F plasmid origin of conjugal DNA transfer, oriT, has been determined. The origin lies in an intercistronic region which contains several inverted repeat sequences and a long AT‐rich tract. Introduction of a nick into one of the DNA strands in the oriT region precedes the initiation of conjugal DNA replication, and the position of the strand‐specific nicks acquired by a lambda oriT genome upon propagation in Flac‐carrying cells has been determined. The nicks were not uniquely positioned, rather there was a cluster of three major and up to 20 minor sites: the biological significance of this observation is not yet fully clear. Nine independent point mutations which inactivate oriT function have been sequenced and found to alter one or other of two nucleotide positions which lie 14 and 19 bp to one side of the rightmost (as drawn) major nick site. These key nucleotides may lie in a recognition sequence for the oriT endonuclease, since mutations at these sites prevent nicking at oriT .

A restriction endonuclease map of EcoRI fragment f6 of F sex factor DNA was constructed and aligned with pre-existing physical and genetic maps. Results of genetic complementation tests and analysis of proteins synthesized in minicells from PstI and BglII sub-fragment clones, or from a specific BglII fragment deletion, have allowed mapping of the locations of the origin of DNA transfer and many of the transfer genes known to lie on f6. The proteins detected account for 78% of the coding capacity of fragment f6.

No abstract