Phosphate Cytidylyltransferase 1, Choline Beta (PCYT1b)

The C terminus of PCYT1B is shorter than that of PCYT1A and has only 3 rather than the 16 serine residues of PCYT1A that are potential phosphorylation sites. Northern blot analysis revealed ubiquitous expression of approximately 6.5-, 1.9-, and 1.1-kb PCYT1B transcripts that were most abundant in testis, placenta, brain, ovary, and all fetal tissues tested. Like PCYT1A, PCYT1B has CT activity that is dependent on the presence of stimulatory lipids. SDS-PAGE and immunoblot analyses indicated that PCYT1B is expressed both as a 35-kD and a 42-kD protein, with an apparent posttranslational modification of the first 26 amino acids accounting for expression of the second form. Immunofluorescence microscopy showed that PCYT1B is localized in the cytoplasm.