Mu bacteriophage genome
Regulation of gene expression
– Repc and Ner regulate the early gene transcription. Repc completely binds the Pe promoter and completely blocks early gene expression, whereas Ner binds the PcM promoter and inhibits Repc expression while negatively regulating Pe in order to keep the level of early genes expression independent of the viral genome copy number.
– Mor positively regulates the middle genes transcription by binding to the Pm promoter .
– C positively regulates the late genes transcription by binding to the Plys, PI, Pp and Pmom (MomP1) promoters. MomP1 is subject to additional positive control by Dam methylation and negative control by the host OxyR function . Com positively regulates the translation of Mom .
– In the absence of C protein, leftward transcription from momP2 occurs .
– Gin is expressed constitutively at a low level and may have its own C-independent promoter and terminate a little bit downstream of momP1 .
– The early operon starts with Ner and presumably ends at the terminator t9.2 in the Pm region .
– The middle operon encode the middle genes and termination occurs immediately downstream of the C gene .
- The lys operon starts with Lys and ends at a terminator in the intergenic region between G and I .
– The I operon starts with protease I and probably encodes a very long transcript which continues through the N gene .
– The P operon terminates in the intergenic regions and between U and U' .
– The Mom operon encodes Com and Mom and probably ends at a terminator located between the mom stop codon and the end of the Mu genome.
NB. A promoter Pgem that would control the expression of GemA and Mor has been suggested, but it is not clear if it exists. If yes, this region could be expressed at a different timing than the other early products .