Histone methyltransferase that specifically di- and trimethylates 'Lys-9' of histone H3 (H3K9me2 and H3K9me3, respectively); involved in positively modulating the rate of age-related behavioral deterioration (PubMed:32103178). May repress the expression of mitochondrial function-related genes by occupying their promoter regions, working in concert with probable chromatin reader protein, baz-2 (PubMed:32103178). Involved in modulation of the mitochondrial unfolded protein response (UPR) (PubMed:32103178). Regulates level of expression of bas-1, a serotonin (5-HT) and dopamine synthesizing enzyme (DOPA decarboxylase) (PubMed:32103178). Negatively modulates levels of endogenous 5-HT and dopamine with aging (PubMed:32103178). Involved in modulating longevity, probably as a result of enhanced stress resistance via mechanisms related to dietary restriction and mitochondrial function (PubMed:32103178). N(6)-methyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6),N(6)-dimethyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-homocysteine N(6),N(6)-dimethyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(9)-[histone H3] + S-adenosyl-L-homocysteine Interacts with baz-2. Broadly expressed in the nervous system, including head, body and tail neurons. Expression increases with age. RNAi-mediated knockdown prevents age-related decline in the expression of bas-1, a serotonin (5-HT) and dopamine synthesizing enzyme (DOPA decarboxylase) (PubMed:32103178). RNAi-mediated knockdown improves behavioral performance in pharyngeal pumping in aged worms (PubMed:32103178). Belongs to the class V-like SAM-binding methyltransferase superfamily.