Unusual transcriptional and translational regulation of the bacteriophage Mu mom operon.
The bacteriophage Mu mom gene encodes a novel DNA modification that protects the viral genome against a wide variety of restriction endonucleases. Expression of mom is subject to a series of unusual regulatory controls. Transcription requires the action of a phage-encoded protein, C, which binds (probably as a dimer) the mom promoter from -33 to -52 (with respect to the transcription start site) in two adjacent DNA major grooves on one face of the helix. No apparent direct interaction between C and the host RNA polymerase (RNAP) is evident; however, C binding alters mom DNA conformation. In the absence of C, RNAP binds the mom promoter at a site that results in transcription in a direction away from the mom gene. The function of this transcription is unknown. An additional layer of transcriptional regulation complexity is due to the fact that the host Dam DNA-(N6-adenine)methyltransferase is required. Dam methylation of three closely spaced upstream GATC sequences is necessary to prevent binding by the host protein, OxyR, which acts as a repressor. Repression is not mediated by inhibition of C binding, but rather through interference with C-mediated recruitment of RNAP to the correct site. Translation of mom is regulated by the phage Com protein. Com is only 62 amino acids long and contains a zinc finger-like structure (coordinated by four cysteine residues) in the amino terminal domain. Com binds mom mRNA 5' to the mom open reading frame, whose translation start signals are contained in a stem-loop translation-inhibition-structure. Com binding to its target site (5' to and adjacent to the translation-inhibition-structure) results in a stable change in RNA secondary structure that exposes the translation start signals.
Hattman
S
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Department of Biology, University of Rochester, NY 14627-0211, USA. modDNA@mail.rochester.edu
D000595:Amino Acid Sequence; D010583:Bacteriophage mu / Q000235:genetics*; D001483:Base Sequence; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D009876:Operon; D014176:Protein Biosynthesis; D012097:Repressor Proteins / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000378:metabolism
C068482:Com protein, Enterobacteria phage Mu; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D004247:DNA; D012321:DNA-Directed RNA Polymerases