Based on the result of sequence analysis,there are three homologues of PCNA in Crenarchaeaon Sulfolobus islandicus and PCNA1 was selected as the subject of the current study.To obtain soluble protein of PCNA1 and its polyclonal antibody for studying the function of PCNA1 gene,the fragment of PCNA1 gene was amplified and cloned into the expression vector pET30a.Induced by IPTG,soluble protein of interest could be obtained.The protein was purified by metal chelate affinity chromatography and its purity and content were detected with UV-spectrophotometric method.Rabbits were immunolized by PCNA1 protein.The titer and specificity of polyclonal antibody were detected with indirect ELISA assay and Western blotting.The result of UV-spectrophotometric method showed that its purity reached at least 90% and the protein concentration was about 2 mg/mL.The titer of antiserum was as high as 1∶10 000,with a very high specificity detected by the Western blotting.