MS_RHII-RSD, a Dual-Function RNase HII-(p)ppGpp Synthetase from Mycobacterium smegmatis

Murdeshwar, Maya S and Chatterji, Dipankar (2012) MS_RHII-RSD, a Dual-Function RNase HII-(p)ppGpp Synthetase from Mycobacterium smegmatis. In: JOURNAL OF BACTERIOLOGY, 194 (15). pp. 4003-4014.

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Abstract

In the noninfectious soil saprophyte Mycobacterium smegmatis, intracellular levels of the stress alarmones guanosine tetraphosphate and guanosine pentaphosphate, together termed (p)ppGpp, are regulated by the enzyme Rel(Msm). This enzyme consists of a single, bifunctional polypeptide chain that is capable of both synthesizing and hydrolyzing (p)ppGpp. The rel(Msm), knockout strain of M. smegmatis (Delta rel(Msm)) is expected to show a (p)ppGpp null (p)ppGpp(0)] phenotype. Contrary to this expectation, the strain is capable of synthesizing (p)ppGpp in vivo. In this study, we identify and functionally characterize the open reading frame (ORF), MSMEG_5849, that encodes a second functional (p)ppGpp synthetase in M. smegmatis. In addition to (p)ppGpp synthesis, the 567-amino-acid-long protein encoded by this gene is capable of hydrolyzing RNA(.)DNA hybrids and bears similarity to the conventional RNase HII enzymes. We have classified this protein as actRel(Msm) in accordance with the recent nomenclature proposed and have named it MS_RHII-RSD, indicating the two enzymatic activities present RHII, RNase HII domain, originally identified as (d) under bar omain of (u) under bar nknown (f) under bar unction 429 (DUF429), and RSD, RelA_SpoT nucleotidyl transferase domain, the SYNTH domain responsible for (p)ppGpp synthesis activity]. MS_RHII-RSD is expressed and is constitutively active in vivo and behaves like a monofunctional (p)ppGpp synthetase in vitro. The occurrence of the RNase HII and (p)ppGpp synthetase domains together on the same polypeptide chain is suggestive of an in vivo role for this novel protein as a link connecting the essential life processes of DNA replication, repair, and transcription to the highly conserved stress survival pathway, the stringent response.

Item Type:	Journal Article
Publication:	JOURNAL OF BACTERIOLOGY
Publisher:	AMER SOC MICROBIOLOGY
Additional Information:	Copyright for this article belongs to the merican Society for Microbiology
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	28 Aug 2012 06:46
Last Modified:	28 Aug 2012 06:46
URI:	http://eprints.iisc.ac.in/id/eprint/44973

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