AU-rich mRNA instability elements on human papillomavirus type 1 late mRNAs and c-fos mRNAs interact with the same cellular factors.

Expression levels of human papillomavirus type 1 late genes are determined in part by an AU-rich inhibitory sequence in the 3' untranslated region on the late mRNAs. Fine mapping of the AU rich inhibitory sequence revealed that it mapped to a 57 nucleotide sequence, consisting of an AU-rich region containing two AUUUA motifs and a U-rich region containing three UUUUU motifs. An internal deletion showed that the U-rich region was required for inhibition. Point mutations in the AUUUA- and UUUUU-motifs inactivated the inhibitory sequence. Analysis of the stability of mRNAs containing the AU-rich sequence in sense or anti-sense orientation showed that mRNAs containing the AU-rich sequence in sense orientation had reduced half life. Analysis of RNA-protein interactions revealed that binding to the inhibitory sequence of three poly(U) binding proteins (38, 44 and 46 kDa) correlated with inhibition and that the same proteins bind to the AU-rich mRNA instability element in the 3' untranslated region on the human c-fos mRNA. We speculate that the human papillomavirus late mRNAs, produced from several hundred copies of the virus genome present in infected cells, compete with the c-fos mRNAs for destabilizing cellular factors and that this may lead to elevated Fos protein levels in human papillomavirus infected cells.