Willment Janet A, Martin Darrin P, Palmer Kenneth E, Schnippenkoetter Wendelin H, Shepherd Dionne N, Rybicki Edward P
Institute of Infectious Diseases and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Observatory 7925, South Africa.
Department of Pharmacology and Toxicology, University of Louisville, 570 South Preston Street, Louisville, KY 40202, USA.
J Gen Virol. 2007 Jun;88(Pt 6):1831-1841. doi: 10.1099/vir.0.82513-0.
The main cis-acting control regions for replication of the single-stranded DNA genome of maize streak virus (MSV) are believed to reside within an approximately 310 nt long intergenic region (LIR). However, neither the minimum LIR sequence required nor the sequence determinants of replication specificity have been determined experimentally. There are iterated sequences, or iterons, both within the conserved inverted-repeat sequences with the potential to form a stem-loop structure at the origin of virion-strand replication, and upstream of the rep gene TATA box (the rep-proximal iteron or RPI). Based on experimental analyses of similar iterons in viruses from other geminivirus genera and their proximity to known Rep-binding sites in the distantly related mastrevirus wheat dwarf virus, it has been hypothesized that the iterons may be Rep-binding and/or -recognition sequences. Here, a series of LIR deletion mutants was used to define the upper bounds of the LIR sequence required for replication. After identifying MSV strains and distinct mastreviruses with incompatible replication-specificity determinants (RSDs), LIR chimaeras were used to map the primary MSV RSD to a 67 nt sequence containing the RPI. Although the results generally support the prevailing hypothesis that MSV iterons are functional analogues of those found in other geminivirus genera, it is demonstrated that neither the inverted-repeat nor RPI sequences are absolute determinants of replication specificity. Moreover, widely divergent mastreviruses can trans-replicate one another. These results also suggest that sequences in the 67 nt region surrounding the RPI interact in a sequence-specific manner with those of the inverted repeat.
玉米条纹病毒（MSV）单链DNA基因组复制的主要顺式作用控制区域据信位于一个约310 nt长的基因间区域（LIR）内。然而，实验上既未确定所需的最小LIR序列，也未确定复制特异性的序列决定因素。在保守的反向重复序列内存在重复序列，即迭代子，这些重复序列在病毒粒子链复制起点处有形成茎环结构的潜力，并且在rep基因TATA框的上游（rep近端迭代子或RPI）。基于对来自其他双生病毒属病毒中类似迭代子的实验分析以及它们与远缘相关的玉米矮花叶病毒中已知Rep结合位点的接近程度，有人提出迭代子可能是Rep结合和/或识别序列。在此，一系列LIR缺失突变体被用于确定复制所需LIR序列的上限。在鉴定出具有不相容复制特异性决定因素（RSD）的MSV毒株和不同的玉米矮花叶病毒后，LIR嵌合体被用于将主要的MSV RSD定位到一个包含RPI的67 nt序列上。尽管结果总体上支持了普遍的假设，即MSV迭代子是其他双生病毒属中发现的那些迭代子的功能类似物，但结果表明反向重复序列和RPI序列都不是复制特异性的绝对决定因素。此外，差异很大的玉米矮花叶病毒可以相互反式复制。这些结果还表明，RPI周围67 nt区域内的序列与反向重复序列的序列以序列特异性方式相互作用。
