Journal of Virology vol:88 issue:18 pages:10501-10
Pseudomonas aeruginosa bacteriophage ФKZ is the type representative of the 'giant' phage genus characterized by unusually large virions and genomes. By unraveling the transcriptional map of the ∼280 kb ФKZ genome to single-nucleotide resolution, we combine 369 ФKZ genes into 134 operons. Early transcription is initiated from highly conserved AT-rich promoters distributed across the ФKZ genome and located on the same strand of the genome. Early transcription does not require phage or host protein synthesis. Transcription of middle and late genes is dependent on protein synthesis and mediated by poorly conserved middle and late promoters. Unique to ФKZ is its ability to complete its infection in the absence of bacterial RNA polymerase (RNAP) enzyme activity. We propose that transcription of the ФKZ genome is performed by the consecutive action of two ФKZ-encoded, non-canonical multisubunit RNAPs, one of which is packed within the virion, another being the product of early genes. This unique, rifampicin-resistant transcriptional machinery is conserved within the diverse giant phage genus.