The mutations ( is allelic to ) and ::Tn completely abolished catabolite repression of gluconate kinase and sorbitol dehydrogenase synthesis in , whereas they only partially affected the catabolite repression of inositol dehydrogenase, histidase and xylose isomerase synthesis. The mutation also partially affected catabolite repression of sporulation. Analysis of revertants from the mutant by direct sequencing indicated that this mutation comprises a base substitution of guanine at nucleotide −14 to adenine within the Shine-Dalgarno sequence of the gene ( translation starts at nucleotide +1). A 1.37 kb RI fragment carrying the gene was cloned into plasmid pUC19 and plasmid pUB110, resulting it plasmids pCCPA19 and pCCPA110, respectively. The gene carried in pCCPA110 complemented the mutation. Western blotting revealed that the level of the CcpA protein in cells, which seemed to be constitutively synthesized, was approximately 10 times lower for the mutant than for the wild-type. The CcpA protein synthesized by either cells bearing pCCPA19 or cells bearing pCCPA110 was purified to over 90% homogeneity; the latter cells were grown in the presence of glucose The molecular mass of the protein purified from was 74 kDa, suggesting that this protein exists as a dimer because its subunit molecular mass was 38 kDa as determined by SDS-PAGE. Gel retardation analysis indicated that the purified CcpA protein in both cases did not bind to the sequence for catabolite repression of the operon, but it bound non-specifically to DNA.


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