ACC EPT

Arginine methylation has been shown to regulate signal transduction, protein subcellular localization, gene transcription and protein-protein interactions that ultimately alter gene expression. Although the role of cellular protein arginine methyltransferases (PRMT) in viral gene expression is largely unknown, we recently showed that the Tat protein of HIV-1 is a substrate for one such enzyme termed PRMT6. However, the mechanism by which arginine methylation impairs the transactivation potential of Tat and the sites of arginine methylation within Tat remain obscure. We now show that Tat is a specific in vitro and in vivo substrate of PRMT6 which targets the Tat R52 and R53 residues for arginine methylation. Such Tat methylation led to decreased interaction with the Tat transactivation region (TAR) of viral RNA. Furthermore, arginine methylation of Tat negatively affected Tat-TAR-cyclin T1 ternary complex formation and diminished cyclin T1-dependent Tat transcriptional activation. Overexpression of wild-type PRMT6, but not a methylase-inactive PRMT6 mutant, reduced levels of Tat transactivation of HIV-1 long terminal repeat (LTR) CAT and luciferase reporter plasmids in a dose-dependent manner. In cell-based assays, knockdown of PRMT6 resulted in increased HIV-