SEQUENCE OF A HUMAN CDNA-ENCODING PHOSPHATIDYLINOSITOL TRANSFER PROTEIN AND OCCURRENCE OF A RELATED SEQUENCE IS WIDELY DIVERGENT EUKARYOTES

Phosphatidylinositol (PtdIns) transfer protein (PtdInsTP) is a phospholipid transfer protein that has been detected in all mammalian tissues examined. It catalyzes the transfer in vitro of PtdIns and phosphatidylcholine between membranes in a number of natural and artificial membrane systems and may be involved in secretion in vivo. In previous studies, we isolated and sequenced a cDNA encoding a rat PtdInsTP. A rat cDNA probe was used to isolate clones from a lambda gt11 human testis cDNA library which encoded full-length human PtdInsTP. The cDNA sequence defines a 270-amino-acid, 31.8-kDa protein whose sequence shares 98.9% identity to that of rat, making it one of the most conserved proteins known between the two species. DNA blot hybridization studies suggest that there may be more than one gene encoding this protein in humans. A comparison of rat and human PtdInsTP cDNAs revealed strong sequence similarity (88 and 84%) in portions of the corresponding 5'- and 3'-untranslated regions (UTR) of the rat and human mRNAs.