Assignment of the gene encoding type 1 gamma protein phosphatase catalytic subunit (PPP1CC) on human, rat, and mouse chromosomes

Cobalamin (vitamin B12) binding, phylogeny, and synteny of human transcobalamin

Selected residues in a highly conserved 15-residue region, 174SVDTAAMAGLAFTC L188 of human transcobalamin (TC), a cobalamin (Cbl: vitamin B12) binding protein, were subjected to site-directed mutagenesis. The mutant constructs were expressed in TC-deficient fibroblasts or in vitro to assess the effect of these mutations on Cbl binding. Phylogenetic analyses and protein parsimony indicated that TC evolved earlier than other mammalian Cbl-binding proteins, intrinsic factor and haptocorrins, and divergence occurred between mouse/rat and human dispersing TC gene to different chromosomes. These studies show that (a) two of the three polar residues, S174, T177, or D176 and two of the three conserved alanine residues, A179 and A184 present in the 15-residue evolutionary conserved region are essential for Cbl-binding by human TC, and (b) TC gene is transferred in a syntenic manner to different chromosomes, at least before the divergence of mouse/rat and human.

Genomic organization and functional analysis of the murine protein phosphatase 1c gamma (Ppp1cc) gene

Protein phosphatase 1 holoenzymes are composed of catalytic subunits in combination with various regulatory subunits. In rodents, four different catalytic isoforms are known, PP1c alpha, -delta, -gamma 1, and -gamma 2. Here we describe the genomic organization of the murine Ppp1cc gene that encodes the PP1c gamma 1 and PP1c gamma 2 isoforms. We determined that Ppp1cc maps to F1.2-G1.2 on chromosome 5 by FISH mapping. Southern hybridization and analysis of cross-hybridizing genomic clones revealed four Ppp1cc-related pseudogenes in the mouse genome. The authentic Ppp1cc gene encodes two isoforms, PP1c gamma 1 and PP1c gamma 2, that arise from alternative splicing and differ by retention of the last intron. The introns of Ppp1cc are flanked by short direct repeats, the significance of which is not clear. Both isoforms retain phosphatase function since they are able to complement the cold-sensitive PP1 defect caused by the dis2-11 mutation in the fission yeast Schizosaccharomyces pombe.