摘要
泡沫病毒的基因转录依赖至少两个不同的启动子 :LTR调节病毒结构蛋白的表达 ,而内部启动子 (IP)则起始调节蛋白mRNA的转录。牛泡沫病毒 (BFV)在env与 3′LTR之间有两个重叠的开放阅读框架orf 1和orf 2 ,分别编码BFVORF 1、ORF 2等多种调节蛋白。这些蛋白中BFVORF 1为转录激活因子 ,称为Tas。Tas对LTR及IP均有反式激活作用。BFV中第二类启动子IP的存在反映了泡沫病毒基因调控的复杂性。已从BFV3 0 2 6中国毒株中克隆了基因组区段 85 72～ 95 0 9,并通过测序和功能分析证明该区段包含了BFVIP。为了对IP进行更精确的定位 ,对其进行了进一步的缺失分析 ,将完整的IP定位在 9117～ 940 5之间。该启动子的TATA盒位于 912 80～92 85 ,是IP必不可少的元件之一。杂合启动子和缺失分析表明 ,TATA盒上游 16 0bp的区域内包含了IP的Tas应答元件 (TREIP) ,其功能类似于增强子。Tas对IP具有强烈的激活作用 ,而C端缺失的ORF 1蛋白或ORF 2蛋白均不足以激活IP的表达。
Foamy viruses are unusual among retroviruses in that they contain two distinct promoter elements. They are the long terminal repeat (LTR) promoter which regulates expression of the viral structural proteins, and a second internal promoter that locates towards the 3' end of the env gene and directs expression of the viral auxiliary proteins. One of these auxiliary proteins is a potent transcriptional transactivator, termed Tas in BFV. That is critical for foamy virus replication. Previously, we have cloned the intact BFV IP and demonstrated it to be highly responsive to the Tas protein. Here, we extended this earlier work by using deleted mutants and hybrid construct to localize the IP more precisely and to identify and characterize the Tas responsive element (TRE IP ) . Based on these data, we propose that genomic region 9117～9405nt contains all the sequences required for full Tas responsiveness. The importance of a TATA box for the BFV internal promoter is established by deletion analysis. The cis-acting sequences in the BFV env gene required for response to Tas are contained within a 160-bp element located 5' to the TATA box in the internal promoter. This Tas responsive element in the internal promoter functions in an orientation-independent fashion in a heterologous promoter and thus has the properties of an enhancer which depends on Tas activity. Alignments reveal that the BFV internal promoter and the BFV LTR have little sequence relatedness. In summary, the genome of bovine foamy virus directs viral transcription through both the promoter in the LTR and an internal promoter within the env gene, and each promoter contains unique enhancer-like elements regulated by the viral transactivator. And it seems that the Tas is the only accessory BFV protein necessary for viral replication in vitro.
出处
《病毒学报》
CAS
CSCD
北大核心
2000年第3期232-237,共6页
Chinese Journal of Virology
基金
国家自然科学基金!( 3 9770 0 3 2 )
天津市自然科学基金!( 983 60 75 11)
关键词
牛泡沫病毒
内部启动子
转录反式激活因子
(Tas)
bovine foamy virus
internal promoter
Tas
Tas responsive element
long terminal repeat promoter
