SUBSTRATE-SPECIFICITY DETERMINANTS IN THE FARNESYLTRANSFERASE BETA-SUBUNIT

Protein prenyltransferases catalyze the covalent attachment of isopren oid lipids (farnesyl or geranylgeranyl) to a cysteine near the C termi nus of their substrates. This study explored the specificity determina nts fur interactions between the farnesyltransferase of Saccharomyces cerevisiae and its protein substrates. A series of substitutions at am ino acid 149 of the farnesyltransferase beta-subunit were tested in co mbination with a series of substitutions at the C-terminal amino acid of CaaX protein substrates Ras2p and a-factor, Efficient prenylation w as observed when oppositely charged amino acids were present at amino acid 149 of the yeast farnesyltransferase beta-subunit and the C-termi nal amino acid of the CaaX protein substrate, but not when like charge s were present at these positions. This evidence for electrostatic int eraction between amino acid 149 and the C-terminal amino acid of CaaX protein substrates leads to the prediction that the C-terminal amino a cid of the protein substrate binds near amino acid 149 of the yeast fa rnesyltransferase beta-subunit.