Heterogeneous nuclear RNP protein A1-arginine methylation during HCT-48 cell cycle.

Abstract

Protein methylase I (protein-arginine N-methyltransferase) was examined in HCT-48 cells, synchronized by serum deprivation and hydroxyurea treatment. The enzyme activity to methylate the added hnRNP protein A1 increased about 2-fold from G0 to S phase, and then decreased during G2/M phase. The enzymatically [methyl-3H]-labeled hnRNP protein A1 was identified by SDS-PAGE/fluorography, and the products were identified as NG-monomethylarginine and NG,NG-dimethyl-(asymmetric)arginines by HPLC. Among endogenous proteins, the 20-kDa species in the extract was most intensely [methyl-3H]-labeled. This 20-kDa methylation was markedly inhibited by the addition of exogenous hnRNP protein A1, indicating that these two substrates compete for the same protein methylase. The possible role of this post-translational modification has been discussed.