Phosphate Cytidylyltransferase 1, Choline Alpha (PCYT1a)

The rate-controlling enzyme in the phosphatidylcholine biosynthetic pathway is CTP-phosphocholine cytidylyltransferase (EC 2.7.7.15). In cultured eukaryotic cells, this enzyme is essential for survival. The alpha isoform is located in the nucleus and is regulated by reversible phosphorylation and membrane association.

The human nucleotide sequence, encoding a 367-amino acid polypeptide, is 89% identical to the rat nucleotide sequence. The catalytic domain of human CTPCT has homology to regions of Bacillus subtilis glycerol phosphate cytidylyltransferase and yeast MUQ1. Kalmar et al. (1994) observed significant identity between the alpha-helical membrane-binding domains of CTPCT and soybean oleosin. Expressed CTPCT had lipid-dependent cytidylyltransferase activity.