Altogether, our results demonstrate that H2AC18 pre-mRNA associates with two distinct populations of the CPSF73/SYMPK endonuclease module, one being aU7 sentitive and active in histone pre-mRNA processing, probably as part of the histone pre-mRNA-processing complex (HCC module), and the other being aU7 insensitive. The gene discussed is H2AC18; the disease is hepatocellular carcinoma.