The human papillomavirus type 1 (HPV-1) late mRNAs contain a 57-nucleotide adenosine- and uridine-rich RNA instability element termed h1ARE in their late 3' untranslated regions. Here we show that five sequence motifs in the h1ARE (named I-V) affect the mRNA half-life in an additive manner. The minimal inhibitory sequence in motifs I and II was mapped to UAUUUAU, and the minimal inhibitory sequence in motifs III-V was mapped to UAUUUUUAU. We also provide evidence that the same motifs in the AU-RNA instability element inhibit mRNA translation, an effect that was entirely dependent on the presence of a poly(A) tail on the mRNA. Additional experiments demonstrated that the h1ARE interacted directly with the poly(A)-binding protein, suggesting that the h1ARE inhibits translation by interfering with the function of the poly(A)-binding protein.