Is the HemK Family of Putative S‐Adenosylmethionine‐Dependent Methyltransferases a “Missing” zeta Subfamily of Adenine Methyltransferases? A Hypothesis

Abstract

Previous comparative studies revealed close similarity among various groups of S‐adenosyl‐L‐methionine (AdoMet)‐dependent methyltransferases (MTases), indicating their common evolutionary origin. We present evidence for a remarkable similarity between the sequence and predicted structure of HemK (a widespread family of putative proteins encoded in genomes from bacteria to humans) and the catalytic domain of the gamma‐subfamily of adenine‐specific DNA MTases (N6mA MTases). We predict the structure and function of the putative catalytic domain of HemK proteins and speculate that the target‐recognizing function may be conferred by the N‐terminal variable region.