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J. Bacteriol., 05 1997, 3298-3303, Vol 179, No. 10
KL Jacobs and DW Grogan
To estimate the efficacy of mechanisms which may prevent or repair thermal
damage to DNA in thermophilic archaea, a quantitative assay of forward
mutation at extremely high temperature was developed for Sulfolobus
acidocaldarius, based on the selection of pyrimidine- requiring mutants
resistant to 5-fluoro-orotic acid. Maximum-likelihood analysis of
spontaneous mutant distributions in wild-type cultures yielded maximal
estimates of (2.8 +/- 0.7) x 10(-7) and (1.5 +/- 0.6) x 10(-7) mutational
events per cell per division cycle for the pyrE and pyrF loci,
respectively. To our knowledge, these results provide the first accurate
measurement of the genetic fidelity maintained by archaea that populate
geothermal environments. The measured rates of forward mutation at the pyrE
and pyrF loci in S. acidocaldarius are close to corresponding rates
reported for protein-encoding genes of Escherichia coli. The normal rate of
spontaneous mutation in E. coli at 37 degrees C is known to require the
functioning of several enzyme systems that repair spontaneous damage in
DNA. Our results provide indirect evidence that S. acidocaldarius has
cellular mechanisms, as yet unidentified, which effectively compensate for
the higher chemical instability of DNA at the temperatures and pHs that
prevail within growing Sulfolobus cells.
Copyright © 1997, American Society for Microbiology
Rates of spontaneous mutation in an archaeon from geothermal environments
Department of Biological Sciences, University of Cincinnati, Ohio 45221- 0006, USA.
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