Analysis of Early Promoters of the Bacillus Bacteriophage GA-1

Bacteriophage GA-1, which infects Bacillus sp. strain G1R, is evolutionarily related to phage φ29, which infects Bacillus subtilis. We report the characterization of several GA-1 promoters located at either end of its linear genome. Some of them are unique for GA-1 and drive the expression of open reading frames that have no counterparts in the genome of φ29 or related phages. These unique promoters are active at early infection times and are repressed at late times. In vitro transcription reactions revealed that the purified GA-1-encoded protein p6 represses the activity of these promoters, although the amount of p6 required to repress transcription was different for each promoter. The level of protein p6 produced in vivo increases rapidly during the first stage of the infection cycle. The protein p6 concentration may serve to modulate the expression of these early promoters as infection proceeds

φ29 Family of Phages

Continuous research spanning more than three decades has made the Bacillus bacteriophage φ29 a paradigm for several molecular mechanisms of general biological processes, such as DNA replication, regulation of transcription, phage morphogenesis, and phage DNA packaging. The genome of bacteriophage φ29 consists of a linear double-stranded DNA (dsDNA), which has a terminal protein (TP) covalently linked to its 5′ ends. Initiation of DNA replication, carried out by a protein-primed mechanism, has been studied in detail and is considered to be a model system for the protein-primed DNA replication that is also used by most other linear genomes with a TP linked to their DNA ends, such as other phages, linear plasmids, and adenoviruses. In addition to a continuing progress in unraveling the initiation of DNA replication mechanism and the role of various proteins involved in this process, major advances have been made during the last few years, especially in our understanding of transcription regulation, the head-tail connector protein, and DNA packaging. Recent progress in all these topics is reviewed. In addition to φ29, the genomes of several other Bacillus phages consist of a linear dsDNA with a TP molecule attached to their 5′ ends. These φ29-like phages can be divided into three groups. The first group includes, in addition to φ29, phages PZA, φ15, and BS32. The second group comprises B103, Nf, and M2Y, and the third group contains GA-1 as its sole member. Whereas the DNA sequences of the complete genomes of φ29 (group I) and B103 (group II) are known, only parts of the genome of GA-1 (group III) were sequenced. We have determined the complete DNA sequence of the GA-1 genome, which allowed analysis of differences and homologies between the three groups of φ29-like phages, which is included in this review