Virus-like Particles and E1AE4 Protein Expressed from the Human Papillomavirus Type 11 Bicistronic E1AE4AL1 Transcript.

Detection of E1AE4 protein in human papillomavirus (HPV 11)-infected tissue is tightly linked to detection of L1 major capsid protein. The only L1-containing transcript identified in HPV 11-infected tissue is the bicistronic E1AE4AL1 mRNA, potentially encoding both the E1AE4 and the L1 proteins. It has not been established that these proteins can be expressed from the E1AE4AL1 transcript. The HPV 11 E1AE4AL1 sequence was cloned by reverse transcriptase polymerase chain reaction into the p1393 vector to produce recombinant baculoviruses. Immunoblots of recombinant baculovirus-infected Sf9 cell lysates demonstrated both the E1AE4 and the L1 proteins. An ELISA was performed on infected Sf9 cells using a monoclonal antibody specific for nondenatured L1, demonstrating that 10 ng of native L1 protein was present per microgram of total nuclear protein. Electron microscopic analysis revealed 50- to 60-nm icosahedral virus-like particles. In vitro transcription/translation was performed using pSPORT constructs containing the E1AE4AL1 sequence or, as controls, monocistronic pSPORT-E1AE4 or L1 constructs. The pSPORT-E1AE4AL1 construct produced the E1AE4 and L1 proteins at a ratio of 17:1. For E1AE4 protein, expression was greater from the pSPORT-E1AE4AL1 construct than from the monocistronic pSPORT-E1AE4 construct. In contrast, more L1 protein was expressed from pSPORT-L1 than from pSPORT-E1AE4AL1. A mutant E1AE4AL1 construct containing no E1AE4 start codon expressed L1 protein in amounts nearly equal to that expressed from the pSPORT-L1 construct. Addition of an antisense oligonucleotide directed at the E1AE4 start codon region to in vitro reactions using pSPORT-E1AE4AL1 was associated with inhibition of E1AE4 protein synthesis and increased translation of L1 protein.