Fig. 1. (A) The C-terminal sequences of HPV18 E6 and two mutants, Thr156Glu and Arg153Leu, are shown, together with the class 1 PDZ-binding consensus sequence and PKA recognition motif. The activities of the wild-type and mutant proteins in Dlg degradation assays (in vitro and in vivo), and their response to PKA activity are shown (Gardiol et al., 1999; Kühne et al., 2000) (our unpublished results). (B) Expression of E6 mRNA in SVJD keratinocytes was analysed by semi-quantitative PCR using primers specific for HPV18 E6 or GAPDH. Equal volumes of the PCR reaction were separated on a 1% agarose-ethidium bromide gel. HPV18 DNA-positive cervical carcinoma cell line, HeLa, and all three E6 lines contained two amplified bands, one of 450 bps corresponding to full-length E6 and a second of 280 bps representing the spliced E6^* product. The position of size markers is shown.