Williams A L
Mol Gen Genet. 1983;191(3):353-7. doi: 10.1007/BF00425745.
Previous findings suggested that cyclic AMP was involved in the regulation of ilvB(AHASI) only and that ilvG (AHASII) and ilvHI (AHASIII) were not controlled by this nucleotide. In this study, derepression patterns of total AHAS activities (ilvB and ilvHI) in adenyl cyclase-negative strains (i.e. cya-) were substantially reduced as contrasted with AHAS activity observed for cya+ strains. Further, the parental strains (cya+) consistently exhibited higher levels of AHAS activity than mutant strains (cya-) during carbon and energy downshifts. Other data suggested that the valine derepression signal could not override the necessity for cya gene product to yield maximal derepression of AHAS gene activities. Cyclic AMP stimulated AHAS gene activities under both in vivo and in vitro assay conditions. Thus, these data provide evidence for an absolute requirement of cAMP for maximal expression of the genes encoding for AHAS activities of E. coli K-12.
先前的研究结果表明，环磷酸腺苷（cAMP）仅参与对ilvB（AHASI）的调控，而ilvG（AHASII）和ilvHI（AHASIII）不受该核苷酸的控制。在本研究中，与cya+菌株中观察到的AHAS活性相比，腺苷酸环化酶阴性菌株（即cya-）中总AHAS活性（ilvB和ilvHI）的去阻遏模式大幅降低。此外，在碳源和能源下降期间，亲本菌株（cya+）始终表现出比突变菌株（cya-）更高水平的AHAS活性。其他数据表明，缬氨酸去阻遏信号无法超越cya基因产物对AHAS基因活性产生最大去阻遏的必要性。在体内和体外测定条件下，环磷酸腺苷均刺激AHAS基因活性。因此，这些数据为环磷酸腺苷对大肠杆菌K-12中编码AHAS活性的基因的最大表达的绝对需求提供了证据。
