Prokaryotic calmodulins: recent developments and evolutionary implications.

Ca2+ is a common intracellular second-messenger molecule in eukaryotic cells and regulates a myriad of cellular processes. Many effects of Ca2+ are mediated by calcium-binding regulatory proteins of the calmodulin superfamily. We propose the idea that calcium-binding proteins originated in high G+C Gram-positive bacteria and were later acquired by eukaryotes.