FIG. 10.

Schematic representation of the HPV-16 genome and potential viral mRNAs. With low levels of PTB, SD36332 is suppressed, presumably by cellular factors binding at SD3632. These unutilized splice sites may retain L2/L1 mRNAs in the nucleus. In the presence of high levels of PTB, the suppression of SD3632 is relieved. This effect results in the production of low levels of L2/L1 mRNAs if silencers at SA5639 (61) are active or high levels of L1 mRNAs if the splicing inhibition at SA5639 is alleviated. LCR, long control region; −PTB, without PTB; +PTB, with PTB. Minus signs in circles indicate cellular factors that bind to HPV-16 mRNAs and inhibit viral RNA splicing (44, 61).