Enables RNA polymerase II transcription regulatory region sequence-specific DNA binding activity and histone methyltransferase activity (H3-K9 specific). Involved in histone H3-K9 methylation; negative regulation of circadian rhythm; and negative regulation of transcription, DNA-templated. Acts upstream of or within several processes, including blastocyst hatching; positive regulation of histone H3-K9 trimethylation; and regulation of cellular response to stress. Located in heterochromatin and nucleus. Part of chromatin silencing complex. Is expressed in several structures, including alimentary system; early conceptus; genitourinary system; integumental system; and nervous system. Orthologous to human SUV39H1 (SUV39H1 histone lysine methyltransferase). [provided by Alliance of Genome Resources, Apr 2022]