Protein arginine methyltransferase I: substrate specificity and role in hnRNP assembly.
Prmt1, the major protein arginine methyltransferase in mammalian cells, has been implicated in signal transduction, transcriptional control, and protein trafficking. In the present study, mouse embryonic stem cells homozygous for an essentially null mutation in the Prmt1 gene were used to examine Prmt1 activity and substrate specificity, which by several criteria appeared to be highly specific. First, other methyltransferases did not substitute for the loss of Prmt1 activity. Second, almost all proteins modified by recombinant Prmt1 in vitro were authentic substrates, i.e., proteins rendered hypomethylated by Prmt1 gene disruption. Finally, Prmt1 did not modify the substrates of other methyltransferases from cells treated with methyltransferase inhibitors. Recombinant proteins corresponding to two splice-variants, Prmt1(353) and Prmt1(371), methylated different, proteins in vitro, providing the first evidence for functional differences between the two isoforms. However, the differences in substrate specificity were lost by the addition of an N-terminal His(6) tag. Loss of Prmt1 activity (and hypomethylation of hnRNPs) has no obvious effect on the formation or composition of hnRNP complexes. Finally, methylation of the most abundant Prmt1 substrates appeared to be extensive and constitutive throughout the cell cycle, suggesting the modification does not modulate protein function under normal growth conditions.
Pawlak
Maciej R
MR
Department of Microbiology and Immunology, Room AA5206 MCN, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2363, USA.
Banik-Maiti
Sarbani
S
Pietenpol
Jennifer A
JA
Ruley
H Earl
HE
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004622:Embryo, Mammalian / Q000166:cytology; D004625:Embryo, Nonmammalian; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism*; D007313:Insecta; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D051379:Mice; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D020033:Protein Isoforms; D011484:Protein-Arginine N-Methyltransferases / Q000737:chemistry* / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors
D018076:DNA, Complementary; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D013395:Sucrose; D008780:Methyltransferases; D011484:Protein-Arginine N-Methyltransferases