Laten H M, Majumdar A, Gaucher E A
Biology Department, Loyola University Chicago, 6525 North Sheridan Road, Chicago, IL 60626, USA.
Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):6897-902. doi: 10.1073/pnas.95.12.6897.
The soybean genome hosts a family of several hundred, relatively homogeneous copies of a large, copia/Ty1-like retroelement designated SIRE-1. A copy of this element has been recovered from a Glycine max genomic library. DNA sequence analysis of two SIRE-1 subclones revealed that SIRE-1 contains a long, uninterrupted, ORF between the 3' end of the pol ORF and the 3' long terminal repeat (LTR), a region that harbors the env gene in retroviral genomes. Conceptual translation of this second ORF produces a 70-kDa protein. Computer analyses of the amino acid sequence predicted patterns of transmembrane domains, alpha-helices, and coiled coils strikingly similar to those found in mammalian retroviral envelope proteins. In addition, a 65-residue, proline-rich domain is characterized by a strong amino acid compositional bias virtually identical to that of the 60-amino acid, proline-rich neutralization domain of the feline leukemia virus surface protein. The assignment of SIRE-1 to the copia/Ty1 family was confirmed by comparison of the conceptual translation of its reverse transcriptase-like domain with those of other retroelements. This finding suggests the presence of a proretrovirus in a plant genome and is the strongest evidence to date for the existence of a retrovirus-like genome closely related to copia/Ty1 retrotransposons.
大豆基因组中存在一个由几百个相对同源的拷贝组成的家族，这些拷贝属于一个名为SIRE-1的大型类copia/Ty1逆转录元件。已从大豆基因组文库中获得了该元件的一个拷贝。对两个SIRE-1亚克隆的DNA序列分析表明，SIRE-1在pol开放阅读框（ORF）的3'端与3'长末端重复序列（LTR）之间含有一个长的、不间断的ORF，该区域在逆转录病毒基因组中包含env基因。对这个第二个ORF进行概念性翻译产生了一种70 kDa的蛋白质。对该氨基酸序列进行计算机分析，预测出的跨膜结构域、α螺旋和卷曲螺旋模式与在哺乳动物逆转录病毒包膜蛋白中发现的模式惊人地相似。此外，一个由65个残基组成的富含脯氨酸的结构域，其氨基酸组成偏差与猫白血病病毒表面蛋白的60个氨基酸的富含脯氨酸的中和结构域几乎相同。通过将SIRE-1的逆转录酶样结构域的概念性翻译与其他逆转录元件的进行比较，证实了SIRE-1属于copia/Ty1家族。这一发现表明植物基因组中存在前病毒，是迄今为止存在与copia/Ty1逆转座子密切相关的类逆转录病毒基因组的最有力证据。
