title: Dual role for transactivator protein C in activation of mom promoter of bacteriophage Mu.
abstract: Transactivator C protein of bacteriophage Mu activates the mom gene of the phage by an unusual mechanism. DNA binding by C to its site results in unwinding of the neighboring sequences, realigning the out-of-phase promoter elements to facilitate RNA polymerase (RNAP) binding. High level stimulation of a C-independent constitutive promoter mutant (where RNAP is already bound) by the transactivator suggested an additional mechanism of transcription activation at a step after RNAP recruitment. In this study, we have investigated the various steps of promoter-polymerase interactions during transcription initiation by using both the promoter mutant and a positive control (pc) mutant of C protein. The transactivator does not influence formation of the open complex or its stability after facilitating the RNAP binding. However, at a subsequent step, the protein exerts an important role, enhancing the promoter clearance by increasing the productive RNAP.promoter complex. The pc mutant of the transactivator C is compromised at this step, supporting the additional downstream role for C in mom transcription activation. We suggest that this unusual multistep activation of Pmom has evolved to ensure irreversibility of the switch during the late lytic cycle of the phage.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Atanu
authors.initials: A
authors.lastname: Chakraborty
authors.forename: Valakunja
authors.initials: V
authors.lastname: Nagaraja
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010583:Bacteriophage mu / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D018983:DNA Footprinting; D004279:DNA, Viral / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011486:Protein C / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000032:analysis / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004279:DNA, Viral; D011486:Protein C; D015534:Trans-Activators; D012321:DNA-Directed RNA Polymerases; D003850:Deoxyribonuclease I; D001616:beta-Galactosidase