One more crazy little thing

Stringent response is run by a family of proteins called RelA-SpoT Homologues, RSH, and these come in two flavors: the long ones and the short ones. The long ones have both ppGpp synthesizing and ppGpp hydrolyzing domains, and either both are active, with synthesizing being the dominant one (that would be the ancestral Rel) or both are active, with hydrolyzing being the dominant one (SpoT) or only the synthesizing one is active (RelA). The short RSHs are more variable. They have only one of the domains, so they can either synthesize (SAS, small alarmone synthetase) or hydrolyze (SAH, small alarmone synthetase) ppGpp. What is fun, is that in addition they can have other domains, sometimes with very peculiar functions.

A very peculiar SAS was characterized recently by Maya Murdeshwar and Dipankar Chatterji. They call it MS_RHII-RSD, or, using terminology proposed in our paper with Gemma Atkinson, actRelMsm. This SAS from Mycobacterium smegmatis in addition to the ppGpp synthetic activity has another one, quite unexpected. It has a dedicated domain capable of hydrolyzing DNA:RNA duplexes via its RNAse H domain.

Quite bizarre, quite.


References:


MS_RHII-RSD:  a dual function RNase HII - (p)ppGpp synthetase from Mycobacterium smegmatis. M. Murdeshwar and D. Chatterji. J. Bacteriology, 2012, in press PIMD: 22636779