title: Silencing of toxic gene expression by Fis.
abstract: Bacteria and bacteriophages have evolved DNA modification as a strategy to protect their genomes. Mom protein of bacteriophage Mu modifies the phage DNA, rendering it refractile to numerous restriction enzymes and in turn enabling the phage to successfully invade a variety of hosts. A strong fortification, a combined activity of the phage and host factors, prevents untimely expression of mom and associated toxic effects. Here, we identify the bacterial chromatin architectural protein Fis as an additional player in this crowded regulatory cascade. Both in vivo and in vitro studies described here indicate that Fis acts as a transcriptional repressor of mom promoter. Further, our data shows that Fis mediates its repressive effect by denying access to RNA polymerase at mom promoter. We propose that a combined repressive effect of Fis and previously characterized negative regulatory factors could be responsible to keep the gene silenced most of the time. We thus present a new facet of Fis function in Mu biology. In addition to bringing about overall downregulation of Mu genome, it also ensures silencing of the advantageous but potentially lethal mom gene.
authors.affiliation: Department of Microbiology and Cell Biology, Indian Institute of Science and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560012, India.
authors.forename: Shweta
authors.initials: S
authors.lastname: Karambelkar
authors.forename: Ganduri
authors.initials: G
authors.lastname: Swapna
authors.forename: Valakunja
authors.initials: V
authors.lastname: Nagaraja
mesh_terms: D000217:Acyltransferases / Q000235:genetics*; D001665:Binding Sites; D018983:DNA Footprinting; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D035021:Factor For Inversion Stimulation Protein / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics*
chemical_list: D029968:Escherichia coli Proteins; D035021:Factor For Inversion Stimulation Protein; C501034:Fis protein, E coli; D012097:Repressor Proteins; D014764:Viral Proteins; D000217:Acyltransferases; C526640:Mu Mom protein, bacteriophage Mu; D012321:DNA-Directed RNA Polymerases