Leaky transcription termination produces larger and smaller than genome size hepatitis B virus X gene transcripts.
The genomic DNA of hepatitis B virus (HBV) is circular and has only one known transcription termination site. The HBV X protein coding sequence is flanked by this transcription termination site at the 3' end and a promoter element at the 5' end. Transcription initiating from the X promoter and terminating at the termination site would produce a transcript 0.7 kb in length, which we have detected in cell lines that produce HBV particles. Unexpectedly, a 3.9-kb transcript containing two copies of the X gene sequence was also detected in these cell lines. Polymerase chain reaction analysis indicates that this 3.9-kb transcript contains sequences from both upstream and downstream of the termination site. Thus, transcription of this 3.9-kb transcript initiates from the X promoter, reads through the termination site, and terminates the second time it encounters the site. Analysis using an SV40-derived vector indicates that the transcription termination site in the HBV genome is also leaky for X gene transcription when a heterologous promoter initiates the transcription. Based on these results, the mechanism of how the transcription termination of HBV mRNA is regulated is discussed.
Guo
W T
WT
Department of Microbiology, University of Southern California, Los Angeles 90033.
Wang
J
J
Tam
G
G
Yen
T S
TS
Ou
J S
JS
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015152:Blotting, Northern; D002460:Cell Line; D005814:Genes, Viral; D006515:Hepatitis B virus / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics*; D014158:Transcription, Genetic; D054334:Viral Regulatory and Accessory Proteins
D012333:RNA, Messenger; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein