A novel nuclear human poly(A) polymerase (PAP), PAP gamma.
Poly(A) polymerase (PAP) is present in multiple forms in mammalian cells and tissues. Here we show that the 90-kDa isoform is the product of the gene PAPOLG, which is distinct from the previously identified genes for poly(A) polymerases. The 90-kDa isoform is referred to as human PAP gamma (hsPAP gamma). hsPAP gamma shares 60% identity to human PAPII (hsPAPII) at the amino acid level. hsPAP gamma exhibits fundamental properties of a bona fide poly(A) polymerase, specificity for ATP, and cleavage and polyadenylation specificity factor/hexanucleotide-dependent polyadenylation activity. The catalytic parameters indicate similar catalytic efficiency to that of hsPAPII. Mutational analysis and sequence comparison revealed that hsPAP gamma and hsPAPII have similar organization of structural and functional domains. hsPAP gamma contains a U1A protein-interacting region in its C terminus, and PAP gamma activity can be inhibited, as hsPAPII, by the U1A protein. hsPAPgamma is restricted to the nucleus as revealed by in situ staining and by transfection experiments. Based on this and previous studies, it is obvious that multiple isoforms of PAP are generated by three distinct mechanisms: gene duplication, alternative RNA processing, and post-translational modification. The exclusive nuclear localization of hsPAP gamma establishes that multiple forms of PAP are unevenly distributed in the cell, implying specialized roles for the various isoforms.
Kyriakopoulou
C B
CB
Department of Cell and Molecular Biology, Uppsala University, Box 596, Uppsala SE-75124, Sweden.
Nordvarg
H
H
Virtanen
A
A
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D002467:Cell Nucleus / Q000201:enzymology*; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D020033:Protein Isoforms; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D000596:Amino Acids; D020033:Protein Isoforms; D011994:Recombinant Proteins; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase