Abstract
DNA methylation regulates many processes, including gene expression, by superimposing secondary information on DNA sequences. The conserved CcrM enzyme, which methylates adenines in GANTC sequences, is essential to the viability of several Alphaproteobacteria. In this study, we find that Caulobacter crescentus cells lacking the CcrM enzyme accumulate low levels of the two conserved FtsZ and MipZ proteins, leading to a severe defect in cell division. This defect can be compensated by the expression of the ftsZ gene from an inducible promoter or by spontaneous suppressor mutations that promote FtsZ accumulation. We show that CcrM promotes the transcription of the ftsZ and mipZ genes and that the ftsZ and mipZ promoter regions contain a conserved CGACTC motif that is critical to their activities and to their regulation by CcrM. In addition, our results suggest that the ftsZ promoter has the lowest activity when the CGACTC motif is non-methylated, an intermediate activity when it is hemi-methylated and the highest activity when it is fully methylated. The regulation of ftsZ expression by DNA methylation may explain why CcrM is essential in a subset of Alphaproteobacteria.
Highlights
DNA methylation regulates many processes in eukaryotes and prokaryotes by superimposing secondary information on the DNA sequence
We find that Caulobacter crescentus cells lacking the CcrM enzyme accumulate low levels of the two conserved FtsZ and MipZ proteins, leading to a severe defect in cell division
We show that CcrM promotes the transcription of the ftsZ and mipZ genes and that the ftsZ and mipZ promoter regions contain a conserved CGACTC motif that is critical to their activities and to their regulation by CcrM
Summary
DNA methylation regulates many processes in eukaryotes and prokaryotes by superimposing secondary information on the DNA sequence. In Gammaproteobacteria, the conservation of Dam may be explained by its involvement in several key cellular processes, such as DNA repair, transcriptional regulation or the initiation of DNA replication (Wion and Casadesus, 2006; Low and Casadesus, 2008; Collier, 2009; Marinus and Casadesus, 2009) All of these processes rely on the periodic variation in the methylation state of the adenines in GATC sequences that occurs upon DNA replication. In other Gammaproteobacteria, methylation by Dam is often dispensable in non-stressed growth conditions
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