Cully D F, Ip H S, Cross G A
Cell. 1985 Aug;42(1):173-82. doi: 10.1016/s0092-8674(85)80113-6.
Trypanosoma brucei variant surface glycoprotein (VSG) genes are activated either by duplicative (DA) transposition of the gene to a pre-activated expression site or by nonduplicative (NDA) activation of a previously silent telomeric gene. We have obtained a recombinant clone spanning the 5' barren region of the expression linked copy of the duplicated VSG gene 117a. By DNA sequence and hybridization analyses we have identified a pleomorphic family of 14-25 non-VSG genes that lie upstream of both DA and NDA VSG expression sites. These expression site associated genes (ESAGs) encode 1.2 kb poly(A)+ mRNAs that are specifically transcribed from the active VSG expression telomere in mammalian bloodstream stages of T. brucei but, in common with VSG genes, are not transcribed in procyclic culture forms. cDNA and genomic sequences predict open reading frames that are conserved in the two ESAGs examined.
布氏锥虫可变表面糖蛋白（VSG）基因的激活方式有两种，一种是基因通过重复（DA）转座至一个预先激活的表达位点，另一种是一个先前沉默的端粒基因通过非重复（NDA）激活。我们获得了一个重组克隆，其跨越重复的VSG基因117a的表达连接拷贝的5'贫瘠区域。通过DNA序列和杂交分析，我们鉴定出一个由14 - 25个非VSG基因组成的多态性家族，这些基因位于DA和NDA VSG表达位点的上游。这些表达位点相关基因（ESAGs）编码1.2 kb的聚腺苷酸化（poly(A)+）mRNA，它们在布氏锥虫哺乳动物血流阶段从活跃的VSG表达端粒特异性转录，但与VSG基因一样，在前循环培养形式中不转录。cDNA和基因组序列预测的开放阅读框在所检测的两个ESAGs中是保守的。
