Abstract
Transactivator protein C is required for the expression of bacteriophage Mu late genes from lys, I, P and mom promoters during lytic life cycle of the phage. The mechanism of transcription activation of mom gene by C protein is well understood. C activates transcription at Pmom by initial unwinding of the promoter DNA, thereby facilitating RNA polymerase (RNAP) recruitment. Subsequently, C interacts with the ß' subunit of RNAP to enhance promoter clearance. The mechanism by which C activates other late genes of the phage is not known. We carried out promoter-polymerase interaction studies with all the late gene promoters to determine the individual step of C mediated activation. Unlike at Pmom, at the other three promoters, RNAP recruitment and closed complex formation are not C dependent. Instead, the action of C at Plys, PI, and PP is during the isomerization from closed complex to open complex with no apparent effect at other steps of initiation pathway. The mechanism of transcription activation of mom and other late promoters by their common activator is different. This distinction in the mode of activation (promoter recruitment and escape versus isomerization) by the same activator at different promoters appears to be important for optimized expression of each of the late genes.
Highlights
Bacteriophage Mu utilizes the host RNA polymerase for its transcription
To address whether there is any requirement of transactivator C for the recruitment of RNA polymerase (RNAP) at the lys, I and P promoters, Electrophoretic Mobilist Shift Assay (EMSA) was carried out on the end-labeled late promoter DNA fragments
C exerts an effect at the step of open complex formation, not seen with Pmom
Summary
Bacteriophage Mu utilizes the host RNA polymerase for its transcription. Expression of the genes in phage Mu is regulated in a temporal fashion. The Mu genome is divided into transcription units designated as early, middle and late genes based on their timing of expression during the phage life cycle. Mu late genes that are expressed during the last phase of the lytic cycle, subsequent to the initiation of the phage DNA replication are dependent on C protein for their expression (Fig 1) [1]. Among the four late genes, the lys gene product is required for host cell lysis at the end of the cycle. I gene has been shown to be required for head synthesis and possibly involved in protein scaffolding during head assembly [3,4], while P gene encodes for one of the enzymes involved in the synthesis of phage
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