Chromosomal localization, genomic organization and evolution of the genes encoding human phosphatidylinositol transfer protein membrane-associated (PITPNM) 1, 2 and 3

Eukaryotic proteins containing a phosphatidylinositol transfer (PITP) domain can be divided into two groups, one consisting of small soluble 35-kDa proteins and the other those that are membrane-associated and show sequence similarities to the Drosophila retinal degeneration B (rdgB) protein. The rdgB protein consists of four domains, an amino terminal PITP domain, a Ca(2+)-binding domain, a transmembrane domain and a carboxyl terminal domain that interacts with the protein tyrosine kinase PYK2. Three mammalian phosphatidylinositol transfer protein membrane-associated genes (PITPNM1, 2 and 3) with homology to Drosophila rdgB have previously been described and shown to be expressed in the mammalian retina. These findings and the demonstration that the rdgB gene plays a critical role in the invertebrate phototransduction pathway have led to the mammalian genes being considered as candidate genes for human eye diseases. In order to facilitate the analysis of these genes we have used radiation hybrid mapping and fluorescence in situ hybridization to localize the PITPNM2 and 3 genes to human chromosomes 12p24 and 17p13 respectively and hybrid mapping to confirm the localization of PITPNM1 to chromosome 11q13. We have also determined the genomic organization of both the soluble and membrane-associated Drosophila and human PITP domain-containing genes. Phylogenetic analysis indicates that the two groups arose by gene duplication that occurred very early in animal evolution