Polymorphism of the yeast pyruvate carboxylase 2 gene and protein: effects on protein biotinylation

Abstract

In Saccharomyces cerevisiae there are two isoenzymes of pyruvate carboxylase (Pyc) encoded by separate genes designated PYC1 and PYC2. We report the isolation and sequencing of a PYC2 gene, and the localization of both genes on the physical map of S. cerevisiae. Comparison with the previously reported sequence [Stucka, Dequin, Salmon and Gancedo (1991) Mol. Gen. Genet. 229, 307-315] revealed significant differences within the open reading frame. The most notable difference was near the 3′ end, where we found a single base deletion reducing the open reading frame by 15 bases. We have confirmed the C-terminus of Pyc2 encoded by the gene isolated here by expressing and purifying an 86-amino-acid biotin-domain peptide. In addition, we investigated the effects of the two changes in the Pyc2 biotin domain (K1155R substitution and Q1178P/five-amino-acid extension) on the extent of biotinylation in vivo by Escherichia coli biotin ligase, and compared the biotinylation of peptides containing these changes with that of two different-length Pyc1 biotin-domain peptides. The K1155R substitution had very little effect on biotinylation, but the five-amino-acid C-terminal extension to Pyc2 and the N-terminal extension to Pycl both improved biotinylation in vivo.