HemK, a class of protein methyl transferase with similarity to DNA methyl transferases, methylates polypeptide chain release factors, and hemK knockout induces defects in translational termination

摘要: HemK, a universally conserved protein of unknown function, has high amino acid similarity with DNA-(adenine-N6) methyl transferases (MTases). A certain mutation in hemK gene rescues the photosensitive phenotype ferrochelatase-deficient (hemH) mutant Escherichia coli. knockout strain E. coli not only suffered severe growth defects, but also showed global shift expression to anaerobic respiration, as determined by microarray analysis, and this may lead abrogation photosensitivity reducing oxidative stress. Suppressor mutations that abrogated defects were isolated shown be caused threonine alanine change at codon 246 polypeptide chain release factor (RF) 2, indicating plays role translational termination. Consistent such role, an enhanced rate read-through nonsense codons induction transfer-mRNA-mediated tagging proteins within cell. By analysis methylation RF1 RF2 vivo vitro, we HemK methylates vitro tryptic fragment containing GGQ motif, is required for same of, least, vivo. This example MTase DNA motif protein-(glutamine-N5) MTase.