Nuclear actin has been elusive due to the lack of molecular mechanisms. From actin-containing chromatin remodeling complexes, we discovered an arginine mono-methylation mark on evolutionarily conserved R256 residue of actin (R256me1). Actin R256 mutations in yeast affect nuclear functions, and cause diseases in human. Interestingly, we show that an antibody specific for actin R256me1 preferentially stain nuclear actin over cytoplasmic actin in yeast, mouse and human cells. We also show that actin R256me1 is regulated by protein arginine methyl transferase-5 (PRMT5) in HEK293 cells. Genome-wide survey of actin R256me1 mark provides a landscape for nuclear actin correlated with transcription. Further gene expression and protein interaction studies uncover extensive correlations between actin R256me1 and active transcription. The discovery of actin R256me1 mark suggests a fundamental mechanism to distinguish nuclear actin from cytoplasmic actin through post-translational modification (PTM), and potentially implicates an actin PTM mark in transcription and human diseases. Overall design: Three biological replciates for either WT or R256C ( a pathogenic mutant in human ? actin causing cerebral and aortic aneurysms) were collected for RNA extraction and subjected to RNA-Seq analysis and gene set enrichment analysis to identify differentially expressed gene sets