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J. Bacteriol. doi:10.1128/JB.00138-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cyclic AMP in Mycobacteria: characterization and functional role of the Rv1647 ortholog in Mycobacterium smegmatis

Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012

^* To whom correspondence should be addressed. Email: sandhya{at}mrdg.iisc.ernet.in.

	Abstract

Mycobacterial genomes are endowed with many eukaryotic-like nucleotide cyclase genes, encoding proteins that can synthesize 3',5'-cAMP. However, the roles of cAMP and the need for such redundancy in terms of adenylyl cyclase genes remain unknown. We measured cAMP in M. smegmatis during growth and under various stress conditions and report the first biochemical and functional characterization of the MSMEG_3780 adenylyl cyclase, whose orthologs in M. tuberculosis (Rv1647) and M. leprae (ML1399) have been recently characterized in vitro. MSMEG_3780 was important for producing cAMP levels in the logarithmic phase of growth, since the MSMEG_3780 strain showed lower intracellular cAMP levels at this stage of growth. Cyclic AMP levels decreased in wild type M. smegmatis on acid stress but not in the MSMEG_3780 strain. This was correlated with a reduction in MSMEG_3780 promoter activity, indicating that the reduction in cAMP on acid stress was caused by a decrease in transcription of MSMEG_3780. Complementation of the MSMEG_3780 strain with genomic integration of MSMEG_3780 or the Rv1647 gene could restore cAMP levels during logarithmic growth. The Rv1647 promoter was also acid sensitive, emphasizing the biochemical and functional similarity in these two adenylyl cyclases. This study therefore represents the first detailed biochemical and functional analysis of an adenylyl cyclase that is important in maintaining cAMP levels in mycobacteria, and underscores the subtle roles these genes may play in the physiology of the organism.