DNA supercoiling, DNA hairpins and single-stranded DNA binding proteins in bacteriophage N4 transcription regulation

Abstract

Transcription of the 72kbp linear double-stranded genome of coliphage N4 is regulated through the sequential utilization of three different DNA-dependent RNA polymerases. A virion-encapsulated, phage-coded RNA polymerase, injected into the host with the viral genome, is responsible for the synthesis of early viral transcripts. Virion RNA polymerase recognizes both a small DNA hairpin and specific sequences on the template strand; promoter recognition on double-stranded DNA requires supercoiled template and E. coli single-stranded DNA binding protein (EcoSSB). A second phage-coded transcriptional machinery synthesizes viral middle transcripts. Finally, the viral single-stranded DNA binding protein allows the E. coli RNA polymerase σ 70 -holoenzyme) to utilize viral late promoters efficiently. Recent evidence about the formation and existence of unusually stable DNA hairpins at virion RNA polymerase promoters, the involvement of these DNA hairpins in N4 virion RNA polymerase-promoter recognition, as well as the novel role of ssDNA binding proteins as transcriptional activators is reviewed.