Regulation of Salmonella enterica pathogenicity island 1 by DNA adenine methylation.
DNA adenine methylase (Dam(-)) mutants of Salmonella enterica are attenuated in the mouse model and present multiple virulence-related defects. Impaired interaction of Salmonella Dam(-) mutants with the intestinal epithelium has been tentatively correlated with reduced secretion of pathogenicity island 1 (SPI-1) effectors. In this study, we show that S. enterica Dam(-) mutants contain lowered levels of the SPI-1 transcriptional regulators HilA, HilC, HilD, and InvF. Epistasis analysis indicates that Dam-dependent regulation of SPI-1 requires HilD, while HilA, HilC, and InvF are dispensable. A transcriptional hilDlac fusion is expressed at similar levels in Dam(+) and Dam(-) hosts. However, lower levels of hilD mRNA are found in a Dam(-) background, thus providing unsuspected evidence that Dam methylation might exert post-transcriptional regulation of hilD expression. This hypothesis is supported by the following lines of evidence: (i) lowered levels of hilD mRNA are found in Salmonella Dam(-) mutants when hilD is transcribed from a heterologous promoter; (ii) increased hilD mRNA turnover is observed in Dam(-) mutants; (iii) lack of the Hfq RNA chaperone enhances hilD mRNA instability in Dam(-) mutants; and (iv) lack of the RNA degradosome components polynucleotide phosphorylase and ribonuclease E suppresses hilD mRNA instability in a Dam(-) background. Our report of Dam-dependent control of hilD mRNA stability suggests that DNA adenine methylation plays hitherto unknown roles in post-transcriptional control of gene expression.
López-Garrido
Javier
J
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Seville 41080, Spain.
Casadesús
Josep
J
D000225:Adenine; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D044404:Genomic Islands / Q000502:physiology*; D051379:Mice; D009154:Mutation; D020871:RNA Stability / Q000502:physiology*; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D019779:Salmonella enterica / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D012329:RNA, Bacterial; D014157:Transcription Factors; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D000225:Adenine