The E1 boolean AND E4 protein of human papillomavirus type 16 associates with a putative RNA helicase through sequences in its C terminus

Human papillomavirus type 16 (HPV16) infects cervical epithelium and is ass ociated with the majority of cervical cancers. The E1 boolean AND E4 protei n of HPV16 but not those of HPV1 or HPV6 was found to associate with a nove l member of the DEAD box protein family of RNA helicases through sequences in its C terminus. This protein, termed E4-DBP (E4-DEAD box protein), has a molecular weight of 66,000 (66K) and can shuttle between the nucleus and t he cytoplasm. It binds to RNA in vitro, including the major HPV16 late tran script (E1 boolean AND E4.L1), and has an RNA-independent ATPase activity w hich can be partially inhibited by E1 boolean AND E4. E4-DBP was detectable in the cytoplasm of cells expressing HPV16 E1 boolean AND E4 (in vivo and in vitro) and could be immunoprecipitated as an E1 boolean AND E4 complex f rom cervical epithelial cell lines. In cell lines lacking cytoplasmic inter mediate filaments, loss of the leucine cluster-cytoplasmic anchor region of HPV16 E1 boolean AND E4 resulted in both proteins colocalizing exclusively to the nucleoli, Two additional HPV16 E1 boolean AND E4-binding proteins, of 80K and 50K, were identified in pull-down experiments but were not recog nized by antibodies to E4-DBP or the conserved DEAD box motif. Sequence ana lysis of M-DBP revealed homology in its E4-binding region with three Escher ichia coli DEAD box proteins involved in the regulation of mRNA stability a nd degradation (RhIB, SrmB, and DeaD) and with the Rrp3 protein of Saccharo myces cerevisiae, which is involved in ribosome biogenesis. The synthesis o f HPV16 coat proteins occurs after E1 boolean AND E4 expression and genome amplification and is regulated at the level of mRNA stability and translati on. Identification of E4-DBP as an HPV16 E1 boolean AND E4-associated prote in indicates a possible role for E1 boolean AND E4 in virus synthesis.