Cloning and expression of the Escherichia coli glgC gene from a mutant containing an ADPglucose pyrophosphorylase with altered allosteric properties.

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A mutant strain of Escherichia coli K-12, designated 618, accumulates glycogen at a faster rate than wild-type strain 356. The mutation affects the ADPglucose pyrophosphorylase regulatory properties (N. Creuzat-Sigal, M. Latil-Damotte, J. Cattaneo, and J. Puig, p. 647-680, in R. Piras and H. G. Pontis, ed., Biochemistry of the Glycocide Linkage, 1972). The enzyme is less dependent on the activator, fructose 1,6 bis-phosphate for activity and is less sensitive to inhibition by the inhibitor, 5'-AMP. The structural gene, glgC, for this allosteric mutant enzyme was cloned into the bacterial plasmid pBR322 by inserting the chromosomal DNA at the PstI site. The glycogen biosynthetic genes were selected by cotransformation of the neighboring asd gene into an E. coli mutant also defective in branching enzyme (glgB) activity. Two recombinant plasmids, pEBL1 and pEBL3, that had PstI chromosomal DNA inserts containing glgC and glgB were isolated. Branching enzyme and ADPglucose pyrophosphorylase activities were increased 240- and 40-fold, respectively, in the asd glgB mutant, E. coli K-12 6281. The E. coli K-12 618 mutant glgC gene product was characterized after transformation of an E. coli B ADPglucose pyrophosphorylase mutant with the recombinant plasmid pEBL3. The kinetic properties of the cloned ADPglucose pyrophosphorylase were similar to those of the E. coli K-12 618 enzyme. The inserted DNA in pEBL1 was arranged in opposite orientation to that in pEBL3.

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