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A novel nuclear human poly(A) polymerase (PAP), PAP gamma
C B Kyriakopoulou1, H Nordvarg, A Virtanen
1Department of Cell and Molecular Biology, Uppsala University, Box 596, Uppsala SE-75124, Sweden.
The Journal of Biological Chemistry
|June 30, 2001
Summary
Researchers identified a new 90-kDa poly(A) polymerase (PAP) isoform, human PAP gamma (hsPAP gamma), encoded by PAPOLG. This nuclear enzyme exhibits distinct properties and specialized roles, contributing to the diverse functions of PAPs in mammalian cells.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Poly(A) polymerase (PAP) exists in multiple forms within mammalian cells and tissues.
- Previous studies identified genes for PAPs, but a distinct 90-kDa isoform was not fully characterized.
Purpose of the Study:
- To identify and characterize the 90-kDa PAP isoform.
- To determine its gene of origin and functional properties.
- To investigate its cellular localization and compare it to other PAP isoforms.
Main Methods:
- Gene cloning and sequencing (PAPOLG identified as the gene for the 90-kDa isoform).
- Biochemical assays to assess enzymatic activity (ATP specificity, cleavage and polyadenylation specificity factor/hexanucleotide-dependent activity).
- Mutational analysis and sequence comparison with hsPAPII.
- In situ staining and transfection experiments for cellular localization.
Main Results:
- The 90-kDa PAP isoform, designated human PAP gamma (hsPAP gamma), is encoded by the PAPOLG gene.
- hsPAP gamma shares 60% amino acid identity with hsPAPII and exhibits similar catalytic efficiency and domain organization.
- hsPAP gamma possesses U1A protein-interacting and inhibitory regions, similar to hsPAPII.
- hsPAP gamma is exclusively localized to the nucleus.
Conclusions:
- Multiple PAP isoforms are generated through gene duplication, alternative RNA processing, and post-translational modification.
- The distinct nuclear localization of hsPAP gamma suggests specialized roles for different PAP isoforms within the cell.
- The discovery of hsPAP gamma expands our understanding of PAP diversity and its functional implications in mammalian cells.