PCNA and progeroid features-hepatocellular carcinoma predisposition syndrome: Thirdly, further co-immunoprecipitation experiments from HEK293 cells expressing SPRTN-wt or the RJALS patient protease defective variant SPRTN Y117C, confirmed that both form a physical complex with CHK1, PCNA and MCM356, further indicating that SPRTN and CHK1 are components of the DNA replication machinery (Fig. 4f).