Effect of the preS1 RNA sequence on the efficiency of the hepatitis B virus preS2 and S protein translation.

The gene coding for hepatitis B virus surface antigen consists of preS1, preS2, and S regions. Two species of mRNAs of this gene are transcribed. The larger species covers all three regions and is translated solely into preS1 protein, whereas the smaller one covers the preS2 and S regions and is translated into preS2 and S proteins. This study examines the influence of the 5' upstream sequence lying in the preS1 region on the synthesis of preS2 and S proteins. For this purpose, several expression plasmids were constructed by inserting various portions of the preS1 region between the retroviral LTR promoter and the preS2/S coding region, and preS2/S protein production was examined in the transfected CHL cells. All the transcripts were initiated in the LTR. A sequence located in the region between 102 and 38 nucleotides upstream from the preS2 initiation codon was found to reduce the production of preS2/S proteins probably at the level of translation. Expression of the heterologous chloramphenicol acetyltransferase gene was similarly inhibited when it was placed downstream of the preS1-102/-38 sequence.