CcrM (or M.CcrMI) is an orphan DNA methyltransferase, that is involved in controlling gene expression in most Alphaproteobacteria. This enzyme modifies DNA by catalyzing the transference of a methyl group from the S-adenosyl-L methionine substrate to the N6 position of an adenine base in the sequence 5-GANTC-3 with high specificity. In some lineages such as SAR11, the homologous enzymes possess 5-GAWTC-3 specificity. In Caulobacter crescentus Ccrm is produced at the end of the replication cycle when Ccrm recognition sites are hemimethylated, rapidly methylating the DNA. CcrM is essential in other Alphaproteobacteria but its role is not yet determined. CcrM is a highly specific methyltransferase with a novel DNA recognition mechanism.