Φ29 phage

Φ29 (Phi 29) belongs to a family of related Bacteriophages which includes, in addition to Φ29, phages PZA, Φ15, BS32, B103, M2Y (M2), Nf and GA-1. These phages, which form part of the Podoviridae family, are the smallest Bacillus phages isolated to date and are among the smallest known dsDNA phages. Most of these phages infect Bacillus subtilis, but often they also infect other related species such as Bacillus amylolyquefaciens, Bacillus pumilus, and Bacillus licheniformis. Phages of this genus have been sub-classified into three groups based on serological properties, DNA physical maps, peptide maps and partial or complete DNA sequences. The first group includes phages Φ29, PZA, Φ15 and BS32, and the second group includes B103, Nf and M2Y. The most distantly related phage of this family, GA-1, is unable to infect the standard B. subtilis strain 168 and has been placed in a third group. Sequence-analysis of the 16S-rRNA of the host strain of GA-1, G1R, showed that it is most closely related to B. pumilus.

Biology of Φ29
Φ29 is 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.