Protein-histidine N-methyltransferase that specifically mediates 3-methylhistidine (tele-methylhistidine) methylation of actin at 'His-73' (PubMed:30626964). Histidine methylation of actin is required for smooth muscle contraction of the laboring uterus during delivery (PubMed:30626964). Does not have protein-lysine N-methyltransferase activity and probably only catalyzes histidine methylation of actin (PubMed:30626964). L-histidyl-[protein] + S-adenosyl-L-methionine = H(+) + N(tele)-methyl-L-histidyl-[protein] + S-adenosyl-L-homocysteine Interacts with MYOD1. Localizes mainly in the cytoplasm. Prominently expressed in the heart and skeletal muscles and is also detected weakly in the stomach, small intestine, and colon. Expression is repressed by microRNAs miR-15b and miR-322, repressing muscle cell differentiation. 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. Mice are viable, but females display severely decreased litter sizes due to primary maternal dystocia (delayed parturition) that is refractory to ecbolic induction agents (PubMed:30626964). Cells show complete loss of actin histidine methylation (PubMed:30626964). Belongs to the class V-like SAM-binding methyltransferase superfamily. SETD3 actin-histidine methyltransferase family. Was initially reported to have histone methyltransferase activity and methylate 'Lys-4' and 'Lys-36' of histone H3 (H3K4me and H3K36me) (PubMed:21832073). However, this conclusion was based on mass spectrometry data wherin mass shifts were inconsistent with a bona fide methylation event and the histone methyltransferase activity could not be confirmed (PubMed:30626964).