Roles of
Various Regions of the HBV Core Promoter in the Transcription of Precore and
Pregenomic RNA*
CHENG Ping, YOU Zhong-Sheng�L, KONG Yu-Ying and
WANG Yuan
( Shanghai Institute of Biochemistry, the Chinese Academy of Sciences,
Shanghai 200031, China )
Abstract To determine the potential
functions of different regions in the HBV core promoter, several mutants
containing B3 and/or C deletion (p3.6IIΔB3, p3.5IIΔB3, p3.6IIΔC, p3.5IIΔB3C)
have been constructed based on the two HBV transcription units (p3.6II and
p3.5II) which contained ENII/Cp and Cp immediate upstream of the linear HBV
genome, respectively. The functional effects of deletions were assessed with respect
to antigen production, viral mRNA synthesis, and viral DNA replication. When
HepG2 cells were transfected with C deletion mutants, HBeAg became undetectable
in the supernatant while the expression of HBcAg in the cell lysate was
retained. Consistently, precore RNA disappeared but the synthesis of pregenomic
RNA and viral DNA replication could still be observed. On the other hand,
deletions of B3 fragment reduced the expression of HBeAg and HBcAg
significantly, while maintained the synthesis of precore RNA, pregenomic RNA
and viral progeny DNA. The results strongly suggest that both fragment C and
fragment D serve as minimal promoter elements for the transcription initiation
of 3.5 kb RNAs. Notably, the D fragment which contains a novel nuclear factor binding
site close to the start site of pregenomic RNA, is critical for the basal
transcription of pregenomic RNA, which has not been reported previously. B3
plays an important role in the efficient transcription of precore and
pregenomic RNAs, but is not indispensable for their basal transcription.
Key Words hepatitis B virus(HBV)； core promoter(Cp)； HBV transcriptional units； deletion mutants
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