Isoprenylcysteine Carboxyl Methyltransferase (ICMT)

Protein-S-isoprenylcysteine O-methyltransferase is the third of three enzymes that posttranslationally modify isoprenylated C-terminal cysteine residues in certain proteins and target those proteins to the cell membrane. This enzyme localizes to the endoplasmic reticulum. Alternative splicing may result in other transcript variants, but the biological validity of those transcripts has not been determined.

In vitro transfection assays showed that ICMT is the functional human homolog of Ste14. Northern blot analysis detected ubiquitous expression of a 3.6-kb transcript. Transfection studies in Chinese hamster ovary (CHO) and COS-1 cells localized ICMT to the endoplasmic reticulum and nuclear membrane, but not to the plasma membrane.