Primarily catalyzes the formation of cysteine and acetate from O-acetylserine and hydrogen sulfide. Can also catalyze the formation of cysteine and acetate from S-sulfocysteine and hydrogen sulfide and the formation of cyanoalanine and hydrogen sulfide from either S-sulfocysteine or O-acetylserine and hydrogen cyanide. hydrogen sulfide + O-acetyl-L-serine = acetate + L-cysteine Amino-acid biosynthesis; L-cysteine biosynthesis; L-cysteine from L-serine: step 2/2. Homodimer. Belongs to the cysteine synthase/cystathionine beta-synthase family.