Genome sequence and gene expression of Bacillus anthracis bacteriophage Fah

Fah, a lytic bacteriophage of Bacillus anthracis, is used widely in the former Soviet Union to identify anthrax bacteria. Here, we present the analysis of a 37,974 bp sequence of the Fah genome and examine gene expression of the phage in a model host, Bacillus cereus. Half of the Fah genome contains genes coding for structural proteins and host lysis functions in an arrangement typical of Syphoviridae. The other half of the genome contains genes coding for enzymes of viral genome replication and for numerous predicted transcription factors that are likely to regulate viral gene expression. Primer extension, in vitro transcription assays, and gene array analysis identified temporal classes of Fah genes and allowed location of viral promoters. Fah does not execute host transcription shut-off and relies on host RNA polymerase (RNAP) σ^A holoenzyme for transcription of its early and late genes. In addition, Fah encodes a sigma factor, σ^Fah, a close relative of Bacillus sporulation factor σ^F that directs bacterial RNAP to at least one late viral promoter. σ^Fah is negatively regulated by host SpoIIAB, an anti-sigma factor that controls sporulation. Thus, σ^Fah may link phage gene expression to sporulation of the host.