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Published online ahead of print on 24 September 2009 as doi:10.1099/mic.0.033621-0
Microbiology (2009), DOI 10.1099/mic.0.033621-0
© 2009 Society for General Microbiology
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Microbiology 0 (2009), mic.0.033621; DOI  10.1099/mic.0.033621-0
© 2009 Society for General Microbiology

A distinct physiological role of MutY in mutation prevention in mycobacteria

Krishna Kurthkoti, T Srinath, Pradeep Kumar, Vidyasagar S Malshetty, Pau Biak Sang, Ruchi Jain, R Manjunath and Umesh Varshney1

IISc

The oxidative damages to DNA result in the occurrence of 7, 8-dihydro-8-oxoguanine (8-oxoG) in the genome. In eubacteria, repair of such damages is initiated by two major base excision repair enzymes, MutM and MutY. We generated a MutY deficient strain of M. smegmatis to investigate its role in DNA repair. The MutY deficiency in M. smegmatis did not result in either a noteworthy susceptibility to oxidative stress or an increase in the mutation rate. However, the rifampicin resistant isolates of the MutY deficient strain showed distinct mutations in the rifampicin resistance determining region of rpoB. Besides the expected C to A (or G to T) mutations, an increase in A to C (or T to G) mutations was also observed. Biochemical characterization of mycobacterial MutY (M. smegmatis and M. tuberculosis) revealed an expected excision of A opposite 8-oxoG in DNA. Additionally, a detectable excision of G and T opposite 8-oxoG was noted. The MutY formed complexes with DNA containing 8-oxoGxA, 8-oxoGxG or 8-oxoGxT but not 8-oxoGxC pairs. The primer extension reactions in M. smegmatis cell-free extracts suggested error-prone incorporation of nucleotides in DNA. Based on these observations, we discuss the physiological role of MutY in specific mutation prevention in mycobacteria.

1 E-mail: varshney{at}mcbl.iisc.ernet.in






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