Papers in the Biological Sciences


Date of this Version



Journal of Bacteriology, July 1999, p. 3920–3927 Vol. 181, No. 13


Copyright © 1999, American Society for Microbiology. All Rights Reserved.


The existence of a global gene regulatory system in the hyperthermophilic archaeon Sulfolobus solfataricus is

described. The system is responsive to carbon source quality and acts at the level of transcription to coordinate

synthesis of three physically unlinked glycosyl hydrolases implicated in carbohydrate utilization. The specific

activities of three enzymes, an a-glucosidase (malA), a b-glycosidase (lacS), and an a-amylase, were reduced

4-, 20-, and 10-fold, respectively, in response to the addition of supplementary carbon sources to a minimal

sucrose medium. Western blot analysis using anti-a-glucosidase and anti-b-glycosidase antibodies indicated

that reduced enzyme activities resulted exclusively from decreased enzyme levels. Northern blot analysis of

malA and lacS mRNAs revealed that changes in enzyme abundance arose primarily from reductions in

transcript concentrations. Culture conditions precipitating rapid changes in lacS gene expression were established

to determine the response time of the regulatory system in vivo. Full induction occurred within a single

generation whereas full repression occurred more slowly, requiring nearly 38 generations. Since lacS mRNA

abundance changed much more rapidly in response to a nutrient down shift than to a nutrient up shift,

transcript synthesis rather than degradation likely plays a role in the regulatory response.

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