Identification of Functional Region of Helicase Gene Promoter in Bombyx mori Nuclear Polyhedrosis Virus

XIAO Qing-Li, ZHANG Zhi-Fang*, YI Yong-Zhu, HE Jia-Lu, WU Xiang-Fu¹
( Key Laboratory of Silkworm Biotechnology, Ministry of Agriculture, Sericultural Research Institute, Chinese ª¤

Academy of Agricultural Sciences, Zhenjiang 212018, China;¹Institute of Biochemistry and Cell Biology, Shanghai ª¤

Institutes for Biological Sciences, the Chinese Academy of Sciences, Shanghai 200031, China )

Abstract    DNA helicases are essential for replication of baculoviruses. It was found that the helicase gene promoter of Bombyx mori nuclear polyhedrosis virus, including 510 bp upstream of ATG, had both early and late RNA initiation sites and could be recognized by cellular RNA polymerase. Transient expression assays in uninfected Sf-21 cells indicated that the helicase gene promoter could be classified as a delayed-early gene promoter. Deletion analysis by PCR showed that the regulation region of its basic transcription was mainly within -510 to -410 bp upstream of ATG. However, the basic activity was still detected with a deletion to -98 bp relative to ATG. In the presence of viral factors, deletion between -510 to -410 bp relative to ATG did not significantly reduce the promoter activity compared to the full-length promoter (510 bp). The remarkable reduction in the promoter activity was observed with continuous deletions. It suggests, therefore, that cis-acting elements responsive to viral factors are mainly located within the range of -410 to -309 bp upstream of ATG.
Key words    Bombyx moriª«nuclear polyhedrosis virus; helicase gene promoter; transient expression; deletion analysis

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