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OBJECTIVE To explore the mechanism of translation initiation regulation of RPA2 via IRES by UNR and eIF3a.METHODS Biotin pull down assay was taken to study the binding of RPA2 IRES and UNR.UNR was knocked down and overexpressed in H1299,A549 and SK-MES cell lines.Western blot and real-time PCR were used to detect protein level and mRNA level respectively.CO-IP assay was conducted for the interaction of eIF3a and UNR.GST pull down assay was carried out to explore the exact domains.And the domains of eIF3a and UNR binding to RPA2 IRES were explored with EMSA assay.RESULTS UNR protein can bind to RPA2 IRES as well as eIF3a.UNR regulated the protein expression of RPA2 in H1299,A549 and SK-MES cells,and there was no change in RPA2 mRNA.UNR combined with eIF3a via the first domain of UNR and the first domain of eIF3a.UNR bound to RPA2 IRES with the first domain.And there was no sufficient evidence for the binding domain of eIF3a with RPA2 IRES yet.CONCLUSION UNR worked with eIF3a and co-regulate the RPA2 IRES activity and further regulate the expression of protein.This is the possible regulation mechanisms of cellular internal ribosomal entry site affect translation initiation.