PMT3 AND PMT4, 2 NEW MEMBERS OF THE PROTEIN-O-MANNOSYLTRANSFERASE GENE FAMILY OF SACCHAROMYCES-CEREVISIAE

Two genes PMT3 and PMT4 were identified by polymerase chain reaction o f genomic DNA using primers derived from regions of high homology betw een the products of three genes PMT1, PMT2 of Saccharomyces cerevisiae and part of a PMT1 related sequence of Kluyveromyces lactis. Pmt1p an d Pmt2p are mannosyltransferases involved in the transfer of a mannosy l residue from dolichyl phosphate-D-mannose (Dol-P-Man) to seryl and t hreonyl residues in proteins. The products encoded by the PMT3 and PMT 4 genes have almost identical hydropathy profiles in comparison to PMT 1 and PMT2: a hydrophobic N- and C-terminal third each with multiple p otential transmembrane helices and a central hydrophillic part. The pr edicted Pmt3p contains 753 amino acids, four potential N-glycosylation sites and it is significantly homologous to Pmt1p, Pmt2p and Pmt4p. P mt4p contains 762 amino acids and two potential N-glycosylation sites. Northern blot analysis showed a single mRNA transcript of PMT3 and PM T4 of 2.8 kb. Thus PMT3 and PMT4 are two new members of the PMT gene f amily. The pmt4 null mutant the pmt3 pmt4 double null mutant, but not pmt3 null mutant, showed a small but significant shift of chitinase du e to under glycosylation of the enzyme. The triple disruption pmt2 pmt 3 pmt4 and the quadruple disruption result in a lethal phenotype. The EMBL data library Accession Number of PMT3 is X83797 and for PMT4 X837 98.