Human papillomavirus type 18 E1 protein is translated from polycistronic mRNA by a discontinuous scanning mechanism

Papillomaviruses are small double-stranded DNA viruses that replicate episo mally in the nuclei of infected cells, The full-length E1 protein of papill omaviruses is required fur the replication of viral DNA, The viral mRNA fro m which the human papillomavirus type 18 E1 protein is expressed is not kno wn. We demonstrate that in eukaryotic cells, the E1 protein is expressed fr om polycistronic mRNA containing E6, E7, and E1 open reading frames (ORFs), The translation of adjacent E7 and E1 ORFs is not associated; it is perfor med by separate populations of ribosomes, The translation of the downstream E1 gene is preceded by ribosome scanning, Scanning happens at least at the 5' end of the polycistronic mRNA and also approximately 100 bp in front of the E1 gene. Long areas in middle of the mRNA are bypassed by ribosomes, p ossibly by ribosomal "shunting," Inactivation of short minicistrons in the upstream area of the E1 gene did not change the expression level of the E1 gene.