Characterisation and partial purification of cellular factors interacting with a negative element on human papillomavirus type 1 late mRNAs.

We have previously identified and characterized an AU-rich inhibitory RNA element located in the 3' untranslated region on late human papillomavirus type 1 (HPV-1) mRNAs. This sequence is active in the absence of virus proteins and interacts specifically with cellular proteins, which presumably mediate the inhibitory activity. Here we have characterized and partially purified five proteins (80-, 52-, 46-, 44-, and 38-kDa) that interact independently and specifically with an AU-rich inhibitory sequence on HPV-1 late mRNAs. Dephosphorylation of the proteins resulted in loss of RNA binding activity. Proteins similar to the 38-, 44-, and 46-kDa proteins were detected also in murine epithelial cells, whereas proteins corresponding to the 80- and 52-kDa proteins were not. Since the inhibitory HPV-1 sequence is active in murine epithelial cells, the results suggested a role for the 38-, 41, and the 46-kDa proteins in the regulation of HPV-1 late gene expression.