Coordinate transcriptional control in the hyperthermophilic archaeon Sulfolobus solfataricus

The existence of a global gene regulatory system in the hyperthermophilic a rchaeon Sulfolobus solfataricus is described. The system is responsive to c arbon source quality and acts at the level of transcription to coordinate s ynthesis of three physically unlinked glycosyl hydrolases implicated in car bohydrate utilization. The specific activities of three enzymes, an alpha-g lucosidase (malA), a beta-glycosidase (lacS), and an alpha-amylase, were re duced 4-, 20-, and 10-fold, respectively, in response to the addition of su pplementary carbon sources to a minimal sucrose medium. Western blot analys is using anti-alpha-glucosidase and anti-beta-glycosidase antibodies indica ted that reduced enzyme activities resulted exclusively from decreased enzy me levels. Northern blot analysis of malA and lacS mRNAs revealed that chan ges in enzyme abundance arose primarily from reductions in transcript conce ntrations, Culture conditions precipitating rapid changes in lacS gene expr ession were established to determine the response time of the regulatory sy stem in vivo. Full induction occurred within a single generation whereas fu ll repression occurred more slowly, requiring nearly 38 generations. Since lacS mRNA abundance changed much more rapidly in response to a nutrient dow n shift than to a nutrient up shift, transcript synthesis rather than degra dation likely plays a role in the regulatory response.