THE REV PROTEIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 COUNTERACTS THE EFFECT OF AN AU-RICH NEGATIVE ELEMENT IN THE HUMAN PAPILLOMAVIRUS TYPE-1 LATE 3' UNTRANSLATED REGION

We have identified a sequence in the late 3' untranslated region of human papillomavirus type 1 mRNAs that acts posttranscriptionally to repress gene expression. Deletion analysis localized the inhibitory element to an AU-rich sequence between nucleotides 6958 and 6984 on the human papillomavirus type 1 genome. This sequence inhibits gene expression in an orientation-dependent manner. Upon transfection of eucaryotic cells with plasmids containing this sequence, approximately 4-fold-lower cytoplasmic mRNA levels and 64- to 128-fold-lower protein levels were produced compared with those produced by plasmids lacking the inhibitory sequence. Interestingly, providing the constitutive transport element of simian retrovirus type 1 in sense orientation counteracted inhibition exerted by the human papillomavirus type 1 sequence. Inhibition could also be overcome by the presence of human immunodeficiency virus type 1 Rev protein in trans and its target sequence, the Rev-responsive element, in cis. Rev is a nuclear protein and acts by promoting nuclear export of human immunodeficiency virus type 1 mRNAs encoding structural proteins. Our results are consistent with a model for human papillomavirus type 1 late-gene expression in which mRNAs containing human papillomavirus type 1 inhibitory sequences enter a nonproductive route in the nucleus, resulting in inefficient mRNA utilization. Rev directs mRNA containing inhibitory sequences to a productive route by interacting with the Rev-responsive element.