THE SCHIZOSACCHAROMYCES-POMBE CWG2-SUBUNIT OF A GERANYLGERANYLTRANSFERASE TYPE-I REQUIRED FOR BETA-GLUCAN SYNTHESIS( GENE CODES FOR THE BETA)

The product of the Schizosaccharomyces pombe cwg2+ gene is involved in the biosynthesis Of beta-D-glucan. When grown at the non-permissive t emperature, cwg2-1 mutant cells lyse in the absence of an osmotic stab ilizer and display a reduced (1-3)beta-D-glucan content and (1-3)beta- D-glucan synthase activity. The cwg2+ gene was cloned by the rescue of the cwg2-1 mutant phenotype using an S.pombe genomic library and subs equently verified by integration of the appropriate insert into the S. pombe genome. Determination of the nucleotide sequence of this gene r evealed a putative open reading frame of 1065 bp encoding a polypeptid e of 355 amino acids with a calculated M(r) of 40 019. The cwg2+ DNA h ybridizes to a main transcript, the 5' end of which maps to a position 469 bp upstream of the predicted start of translation. The sequence b etween the transcription and the translation start sites is unusually long and has several short open reading frames which suggest a transla tional control of the gene expression. Comparative analysis of the pre dicted amino acid sequence shows that it possesses significant similar ity to three Saccharomyces cerevisiae proteins, encoded by the DPR1/RA M1, CDC43/CAL1 and ORF2/BET2 genes respectively, which are beta subuni ts of different prenyltransferases. When grown at 37-degrees-C, cwg2-1 mutant extracts were specifically deficient in geranylgeranyltransfer ase type I activity, as measured in vitro. Multiple copies of the CDC4 3 gene can partially suppress the growth and (1-3)beta-D-glucan syntha se defect of the cwg2-1 mutant at the restrictive temperature. In a si milar manner, the cwg2+ gene can partially suppress the cdc43-2 growth defect. These results indicate that cwg2+ is the structural gene for the beta subunit of geranylgeranyltransferase type I in S.pombe and th at this enzyme is required for (1-3)beta-D-glucan synthase activity. T he functional homology of Cwg2 with Cdc43, which has been implicated i n the control of cell polarity, suggests a link between two morphogene tic events such as establishment of celt polarity and cell wall biosyn thesis.