-!- This enzyme, along with EC 2.5.1.59 and EC 2.5.1.60, constitutes the protein prenyltransferase family of enzymes. -!- Catalyzes the formation of a thioether linkage between the C-1 of an isoprenyl group and a cysteine residue fourth from the C-terminus of the protein. -!- These protein acceptors have the C-terminal sequence CA(1)A(2)X, where the terminal residue, X, is preferably serine, methionine, alanine or glutamine; leucine makes the protein a substrate for EC 2.5.1.59. -!- The enzymes are relaxed in specificity for A(1), but cannot act if A(2) is aromatic. -!- Substrates of the prenyltransferases include Ras, Rho, Rab, other Ras-related small GTP-binding proteins, gamma-subunits of heterotrimeric G-proteins, nuclear lamins, centromeric proteins and many proteins involved in visual signal transduction.