Jaaskelainen M, Mykkanen AH, Arna T, Vicient CM, Suoniemi A, Kalendar R, Savilahti H, Schulman AH
Plant J. 1999 Nov;20(4):413-22. doi: 10.1046/j.1365-313x.1999.00616.x.
Retrotransposons are ubiquitous and major components of plant genomes, and are characteristically retroviral-like in their genomic structure and in the major proteins encoded. Nevertheless, few have been directly demonstrated to be transcribed or reverse transcribed. The BARE-1 retrotransposon family of barley (Hordeum vulgare) is highly prevalent, actively transcribed, and contains well conserved functional regions. Insertion sites for BARE-1 are highly polymorphic in the barley genome. Here we show that BARE-1 is translated and the capsid protein (GAG) and integrase (IN) components of the predicted polyprotein are processed into polypeptides of expected size. Some of the GAG sediments as virus-like particles together with IN and with BARE-1 cDNA. Reverse transcriptase activity is also present in gradient fractions containing BARE-1 translation products. Virus-like particles have also been visualized in fractions containing BARE-1 components. Thus BARE-1 components necessary for carrying out the life cycle of an active retrotransposon appear to be present in vivo, and to assemble. This would suggest that post-translational mechanisms may be at work to prevent rapid genome inflation through unrestricted integration.
逆转录转座子广泛存在，是植物基因组的主要组成部分，其基因组结构和所编码的主要蛋白质具有典型的类逆转录病毒特征。然而，直接证明其转录或逆转录的却很少。大麦（Hordeum vulgare）的BARE-1逆转录转座子家族高度普遍、活跃转录且包含保守的功能区域。BARE-1在大麦基因组中的插入位点具有高度多态性。在此我们表明BARE-1能够被翻译，预测的多蛋白中的衣壳蛋白（GAG）和整合酶（IN）成分被加工成预期大小的多肽。一些GAG与IN以及BARE-1 cDNA一起以病毒样颗粒的形式沉降。在含有BARE-1翻译产物的梯度组分中也存在逆转录酶活性。在含有BARE-1成分的组分中也观察到了病毒样颗粒。因此，执行活跃逆转录转座子生命周期所需的BARE-1成分似乎在体内存在并组装。这表明可能存在翻译后机制来防止因不受限制的整合导致基因组快速膨胀。
