Continuous research, spanning a period of more than three decades, has made the Bacillus bacteriophage Φ29 a paradigm for the study of several molecular mechanisms of general biological processes, including DNA replication and regulation of transcription. The genome of Φ29 consists of a linear double-stranded (ds) DNA, which has a terminal protein covalently linked to its 5' ends. Initiation of DNA replication, carried out by a protein-primed mechanism, has been studied in detail in vitro and is considered to be a model system that is also used by other linear genomes with a terminal protein linked to their DNA ends. Phage Φ29 has also been proven to be a versatile system to study in vitro transcription regulation in general and the switch from early to late phage transcription in particular. The detailed knowledge of in vitro phage Φ29 DNA replication and transcription regulation makes it an attractive model to study these processes in vivo. For many years it has been known that (i) phage Φ29 DNA replication, as well as that of other prokaryotic genomes, occurs at the cytosolic membrane, and (ii) the lytic Φ29 cycle is suppressed in early sporulating cells and under these conditions the infecting phage genome becomes trapped into the spore. The molecular mechanisms involved in these processes were largely unknown. We review here the advances recently obtained in our understanding of membrane-associated organization of Φ29 DNA replication and the mechanisms underlying the alternative infection strategy.

Peer reviewed