Phanerochaete chrysosporium glyoxal oxidase is encoded by two allelic variants: structure, genomic organization, and heterologous expression of glx1 and glx2

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Abstract
A cDNA clone (glx-2c) encoding glyoxal oxidase (GLOX) was isolated from a Phanerochaete chrysosporium lambda gt11 library, and its nucleotide sequence was shown to be distinct from that of the previously described clone glx-1c (P. J. Kersten and D. Cullen, Proc. Natl. Acad. Sci. USA 90:7411-7413, 1993). Genomic clones corresponding to both cDNAs were also isolated and sequenced. overall nucleotide sequence identity was 98%, and the predicted proteins differed by a single residue: Lys-308<==>Thr-308. Analyses of parental dikaryotic strain BKM-F-1767 and homokaryotic progeny firmly established allelism for these structural variants. Southern blots of pulsed-field gels localized the GLOX gene (glx) to a dimorphic chromosome separate from the peroxidase and cellobiohydrolase genes of P. chrysosporium. Controlled expression of active GLOX was obtained from Aspergillus nidulans transformants when glx-1c was fused to the promoter and secretion signal of the A. niger glucoamylase gene. The GLOX isozyme corresponding to glx-2c was also efficiently secreted by A. nidulans following site-specific mutagenesis of the expression vector at codon 308 of glx-1c.