Investigation Of Bacterial Rna-Directed Dna Methylation Via Dcm And Hfq

INVESTIGATION OF BACTERIAL RNA-DIRECTED DNA METHYLATION VIADCM AND HFQbyDANDAN LIMay 2013 Advisor: Dr Andrew FeigMajor: Chemistry (Biochemistry)Degree: Master of ScienceBacterial small RNAs and the RNA chaperone Hfq play crucial roles inpost-transcriptional gene regulation, often as parts of stress-response pathways,but little is known about their roles in regulation of gene transcription. A recent report showed that changes in methylation patterns caused by DNA cytosinemethyltransferase (Dcm) were linked to gene regulation occurring during thetransition to stationary phase. Here, we show that Dcm involves in the stressresponses under nutrient starvation and cold stress. Dcm and Hfq togethermediate gene expression under cold stress. Hfq promotes Dcm-catalyzedcytosine methylation at specific sites near the rpoS promoter, which is consistent with the genome-wide analysis and linking known stress response pathways toaltered methylation. Overexpressing DsrA, an sRNA induced at low temperatureto regulate genes required for cold adaptation, stimulates this DNA methylationbehavior, showing that the regulation is sRNA-dependent. This represents thefirst example of an RNA-directed DNA methylation mechanism in bacteria responsible for modulating gene expression.