Protein-histidine N-methyltransferase that specifically mediates 3-methylhistidine (tele-methylhistidine) methylation of actin at 'His-73' (PubMed:30526847). Histidine methylation of actin is required for smooth muscle contraction of the laboring uterus during delivery (By similarity). Does not have protein-lysine N-methyltransferase activity and probably only catalyzes histidine methylation of actin (By similarity). L-histidyl-[protein] + S-adenosyl-L-methionine = H(+) + N(tele)-methyl-L-histidyl-[protein] + S-adenosyl-L-homocysteine kcat is 0.8 min(-1) with beta-actin as substrate (PubMed:30526847). kcat is 0.57 min(-1) with S-adenosyl-L-methionine as substrate (PubMed:30526847). Interacts with MYOD1. Localizes mainly in the cytoplasm. The SET domain specifically recognizes and binds actin, suggesting that it does not accommodate substrates diverging from actin. Phosphorylated by GSK3B, which is required for recognition by the SCF(FBXW7) complex and subsequent degradation. Ubiquitinated by the SCF(FBXW7) complex following phosphorylation by GSK3B, leading to its degradation by the proteasome. Belongs to the class V-like SAM-binding methyltransferase superfamily. SETD3 actin-histidine methyltransferase family.