HPV-16 RNA processing.

To understand human papillomavirus type 16 (HPV-16) gene regulation, it is necessary to understand HPV-16 RNA processing. HPV-16 encodes multiple 5'- and 3'-splice sites and two polyadenylation signals pAE and pAL (Figure 1). The major 3'-splice site on the HPV-16 genome (SA3358) is used for generation of E6, E7, E4, L1 and L2 mRNAs. It encodes a suboptimal splice signal but is under control of a strong enhancer that renders SA3358 one of the most efficiently used splice sites on the HPV-16 genome. Thereby SA3358 indirectly blocks HPV-16 late gene expression. The early polyA signal is also under control of the early UTR sequence and multiple RNA elements in the L2 coding region that interact with hnRNP H. The two splice sites SD3632 and SA5639 are used exclusively by late mRNAs and are under control of multiple splicing silencer elements. The silencers at SA5639 are located in the L1 coding region and interact with hnRNP A1. So far, only polypyrimidine tract binding protein (PTB) has been shown to induce late gene expression.