The E2 protein of human papillomavirus type 16 is translated from a variety of differentially spliced polycistronic mRNAs

The major regulation protein of human papillomavirus (HPV) transcription is the viral E2 protein. Previous studies have identified a variety of altern atively spliced mRNAs containing multiple open reading frames (ORFs) encodi ng the E2 protein of HPV type 16. In these mRNAs the E2 ORF is contained as an internal ORF. In the present study, the translational capacities of thr ee mRNA species starting at the p97 promoter and containing the 880/2581, 8 80/2708 and 226/2708 splice junctions upstream of the E2 ORF were investiga ted. Partial cDNAs spanning the E2 ORF and the related upstream ORFs were s ynthesized and assessed for E2 protein translation in vivo, in COS cells, a nd in vitro, in cell-free systems. Results of these analyses indicated that E2 protein was translated from all three mRNAs, Translation efficiency of E2 from the natural polycistronic templates was lower compared with that fr om a synthetic monocistronic control. Translation from the d-type bicistron ic template (226/2708) was more efficient than that from the a-type (880/27 08) and a'-type (880/2561) polycistronic templates. Further investigation o f the translation of proteins encoded by the ORFs preceding the; E2 ORF sho wed that a- and a'-type templates served for translation mainly of E7 but a lso of E61, while the d-type template served for translation of E6IV. Overa ll, the translation data support the suggestion that the corresponding mRNA s may function as polycistronic transcripts.