Heterogeneous nuclear ribonucleoprotein C binds exclusively to the functionally important UUUUU-motifs in the human papillomavirus type-1 AU-rich inhibitory element.

We have previously identified an inhibitory, 57 nt AU-rich sequence in the HPV-1 late 3' UTR, termed as the HPV-1 AU-rich element (h1ARE). It contains two types of functionally important motifs: two AUUUA sequences and three UUUUU sequences. We have shown that the h1ARE interacts with heterogeneous nuclear ribonucleoprotein (hnRNP) C1/C2 and the ELAV-like HuR protein. While we have shown that HuR binds to both the AUUUA- and the UUUUU-motifs, the interaction between hnRNP C and the h1ARE has not been investigated in detail. Here, we have used recombinant (r)hnRNP C1 to study the interaction between hnRNP C1 and the h1ARE by using the UV cross-linking assay. We demonstrate that (r)hnRNP C1 cross-links specifically to the three functionally important UUUUU-motifs in the h1ARE. In contrast, (r)hnRNP does not UV cross-link to the functionally important AUUUA-motifs in the h1ARE. Conclusively, the binding ability of hnRNP C to the h1ARE correlates with its partially inhibitory function. Additionally, the recombinant AU-rich RNA binding factor 1 (AUF1) was analyzed for binding to the h1ARE by using the UV cross-linking assay, but the results revealed no specificity for the functionally important AUUUA- and UUUUU-motifs.