Two cysteine synthase enzymes are found, this enzyme and CysM; both catalyze the same reaction. Cysteine synthase B (CysM) can also use thiosulfate in place of sulfide to give cysteine thiosulfonate as a product. hydrogen sulfide + O-acetyl-L-serine = acetate + L-cysteine O-acetyl-L-serine causes the CysE-CysK complex to dissociate in the absence of hydrogen sulfide. Amino-acid biosynthesis; L-cysteine biosynthesis; L-cysteine from L-serine: step 2/2. Part of the cysteine synthase complex formed at a ratio of 2 copies of this protein and 1 copy of serine acetyltransferase (cysE). The complex reversibly dissociates in the presence of O-acetyl-L-serine but in the absence of hydrogen sulfide (PubMed:4977445). Homodimer (PubMed:10452898, PubMed:11023792, PubMed:9761678). Belongs to the cysteine synthase/cystathionine beta-synthase family.