E6 protein sequences. The secondary structure of E6 protein is shown. The E6 gene codes for full-length E6 as well as a truncated protein (E6*I, indicated in pink). The E6 splice donor mutant (E6MT) was generated by site-directed mutagenesis at the splice donor site resulting in a V to L substitution at amino acid 42 (arrow head). This construct expresses only E6 full-length protein. Whereas, the E6*I construct expresses only the truncated form of E6 and not the full-length form. GFP was fused to the N-terminus of each of these constructs.