A series of hepatitis B virus open reading frame (ORF) variants, including mutants in which the relative order of the in-frame start codons (AUG1, AUG2 and AUG3) and nearby sequences had been altered, was expressed both (in HepG2 hepatoblastoma cells) and (by T7 promoter-driven transcription followed by translation in a rabbit reticulocyte lysate). The ratio of the synthesis of the large, middle (M) and major (S) proteins or their chimeric counterparts was analysed to study the translational regulation of ORF expression. As expected on the basis of the ribosome scanning model, the AUG sequence context was found to be a prominent factor in determining the different translational behaviour of the two -specific mRNAs of 2.4 kb (predominantly translated from AUG1) and 2.1 kb (which includes AUG2 and/or AUG3 and can be translated from either). Results from both experimental systems suggested that initiation at internal AUGs in the 2.4 kb RNA is possible. In experiments mutants bearing lesions in a region 5′ to AUG2, which has been implicated in AUG2/AUG3 cis repression, showed no increase in the utilization of internal AUGs. In addition, the chimeric envelope polypeptides produced in transfected HepG2 cells in this study were informative with respect to preS-mediated endoplasmic retention: replacement of the preS2 N terminus with that from preS1 generated a chimeric M protein that was glycosylated within the putative preS1 retention sequence ad was not secreted. Thus, the preS1 retention sequence most likely acts inside the lumen of endoplasmic reticulum and its function is insensitive to glycosylation. A similar element might be active at the N terminus of M protein.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error