NUCLEOTIDE-SEQUENCE OF THE EXO-1,3-BETA-GLUCANASE-ENCODING GENE, EXG1, OF THE YEAST SACCHAROMYCES-CEREVISIAE

The nucleotide (nt) sequence of the Saccharomyces cerevisiae gene (EXG1) encoding extracellular exo-1,3-beta-glucanases (EXG) I and II was determined. An open reading frame of 1344 bp codes for a 448-amino acid (aa) polypeptide, with a calculated M(r) of 51 307, which contains two potential N-glycosylation sites. The EXG1 DNA hybridizes to a 1.7-kb transcript whose 5' end maps to a position 98 bp upstream from the site of initiation of protein synthesis. Comparison of the N-terminal aa sequence deduced from the nt sequence with that of the purified EXGII revealed the existence of an extra 40-aa peptide in the precursor protein containing a Lys-Arg peptidase-processing site at the junction with the mature, extracellular form. The N-terminal region of the putative precursor is a very hydrophobic segment with structural features resembling those of signal peptides of secreted proteins. The M(r) of the mature EXG polypeptide deduced from the nt sequence is 46 385. The 5'- and 3'-flanking regions of the EXG1 gene have structural features in common with other yeast genes.