Crasnier-Mednansky Martine, Park Maxwell C, Studley William K, Saier Milton H
University of California at San Diego, Department of Biology, La Jolla, CA 92093-0116, USA.
Microbiology (Reading). 1997 Mar;143 ( Pt 3):785-792. doi: 10.1099/00221287-143-3-785.
In Escherichia coli, expression of certain genes and operons, including the fructose operon, is controlled by Cra, the pleiotropic catabolite repressor/activator protein formerly known as FruR. In this study we have demonstrated that cra mutant strains synthesize 10-fold less cAMP than isogenic wild-type strains, specifically when grown in fructose-containing minimal media. The glucose-specific IIA protein (IIAglc) of the phosphotransferase system, which activates adenylate cyclase when phosphorylated, is largely dephosphorylated in cra but not wild-type strains growing under these conditions. Dephosphorylation of IIAglc in cra strains apparently results from enhanced fructose operon transcription and fructose uptake. These conclusions were supported by showing that fructose-grown cra strains possess 2.5-fold higher fructose-1-phosphate kinase activity than fructose-grown wild-type strains. Moreover, artificially increasing fructose operon expression in cells transporting fructose dramatically decreased the activity of adenylate cyclase. The results establish that Cra indirectly regulates the activity of adenylate cyclase by controlling the expression of the fructose operon in cells growing with fructose as the sole carbon source.
在大肠杆菌中，某些基因和操纵子的表达，包括果糖操纵子，受Cra控制，Cra是一种多效性分解代谢物阻遏物/激活蛋白，以前称为FruR。在本研究中，我们证明了cra突变株合成的cAMP比同基因野生型菌株少10倍，特别是在含果糖的基本培养基中生长时。磷酸转移酶系统的葡萄糖特异性IIA蛋白（IIAglc）在磷酸化时激活腺苷酸环化酶，在这些条件下生长的cra菌株中，IIAglc大部分去磷酸化，而野生型菌株中则不然。cra菌株中IIAglc的去磷酸化显然是由于果糖操纵子转录增强和果糖摄取增加所致。这些结论得到了以下结果的支持：以果糖为碳源生长的cra菌株比以果糖为碳源生长的野生型菌株具有高2.5倍的果糖-1-磷酸激酶活性。此外，在转运果糖的细胞中人为增加果糖操纵子的表达会显著降低腺苷酸环化酶的活性。结果表明，在以果糖作为唯一碳源生长的细胞中，Cra通过控制果糖操纵子的表达间接调节腺苷酸环化酶的活性。
