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Baculovirus immediately early 1, a mediator for homologous regions enhancer function in trans | Lin et al. Virology Journal 2010 7 32 http www.virologyj.eom content 7 1 32 VIROLOGY JOURNAL RESEARCH Open Access Baculovirus immediately early 1 a mediator for homologous regions enhancer function in trans Xu ai Lin1 2 Yin Chen 2 Yongzhu Yi2 Zhifang Zhang2 Abstract Background Enhancers are DNA sequences that serve as binding sites for regulatory proteins and stimulate transcriptional activity independent of their positions and orientations with respect to the transcriptional initiation site. Previous studies considered that baculovirus homologous regions hrs function as enhancers in cis. In our study a plasmid containing homologous region 3 hr3 enhancer from Bombyx mori nucleopolyhedrovirus BmNPV failed to enhance transcription of promoter in other plasmid in co-transfection assays but strong stimulation occurred when cells were infected by BmNPV. Results The cotransfection results of each BmNPV genomic library plasmid hr3 plasmid and reporter plasmid showed that there were eight library plasmids stimulated the luciferase gene expression remarkably. Sequencing these plasmids revealed that each of them contained the ie-1 gene. Transfected plasmids containing ie-1 hr3 and various origin promoter drove reporter gene showed the function was even retained. Cotransfection of hr3 functional dissected fragment and ie-1 revealed that the 30-bp imperfect palindrome destroyed fragment can t enhance reporter gene expression even though transfected with ie-1. Conclusion IE-1 was the only early factor of BmNPV that could act as a mediator for hr enhancer function in trans and the trans-function was achieved with a broad-spectrum of promoters. The 30-bp imperfect palindrome was the elementary molecular structure by which IE-1 participated in the enhancer function in trans. Background The genome of baculovirus contains interspersed homologous regions hrs that function as transcriptional enhancers linking in cis to viral or heterologous promoters in either insect or mammalian .