Presting G G, Malysheva L, Fuchs J, Schubert I
Institute of Plant Genetics and Crop Plant Research, Germany.
Plant J. 1998 Dec;16(6):721-8. doi: 10.1046/j.1365-313x.1998.00341.x.
A 745 bp sequence (pSau3A9) located at the centromeres of several cereal species was isolated from a sorghum BAC library by Jiang et al. (1996, Proc. Natl Acad. Sci. USA, 93, 14210-14213). We have amplified a partially homologous 809 bp sequence from barely genomic DNA by PCR and localized it to the centromeres of barley, wheat and rye chromosomes by fluorescent in situ hybridization (FISH). Sequence analysis showed this barley homolog of pSau3A9 to have high similarity to the integrase region of the polyprotein gene of Ty3/gypsy group retrotransposons. Using this integrase sequence as a probe, several clones were isolated from a lambda library constructed of genomic barley DNA. One of the lambda clones contained coding regions for all five catalytic sites characteristic of the retrotransposon polyprotein. Two direct repeats flanking the polyprotein gene are homologous to the cereal centromeric sequence described by Aragón-Alcaide et al. (1996, Chromosoma, 105, 261-268) and may represent all or part of the long-terminal repeats (LTRs). Different plasmid subclones containing various regions of the lambda clone were used in FISH to show that the entire polyprotein gene and upstream flanking sequences, including the presumed LTR, are present at barley centromeres. The preferential (or exclusive) localization of an apparently complete retroelement within the centromeric regions of several cereal species raises interesting questions about its role in karyotype evolution and centromere function.
Jiang等人（1996年，《美国国家科学院院刊》，93卷，14210 - 14213页）从高粱BAC文库中分离出一段位于几种谷类物种着丝粒的745 bp序列（pSau3A9）。我们通过PCR从大麦基因组DNA中扩增出一段部分同源的809 bp序列，并通过荧光原位杂交（FISH）将其定位到大麦、小麦和黑麦染色体的着丝粒上。序列分析表明，pSau3A9的这个大麦同源序列与Ty3/gypsy组逆转座子多蛋白基因的整合酶区域具有高度相似性。以这个整合酶序列为探针，从由大麦基因组DNA构建的λ文库中分离出了几个克隆。其中一个λ克隆包含逆转座子多蛋白所有五个催化位点的编码区。多蛋白基因两侧的两个直接重复序列与Aragón - Alcaide等人（1996年，《染色体》，105卷，261 - 268页）描述的谷类着丝粒序列同源，可能代表长末端重复序列（LTRs）的全部或部分。含有λ克隆不同区域的不同质粒亚克隆用于FISH，以表明整个多蛋白基因和上游侧翼序列，包括推测的LTR，都存在于大麦着丝粒上。一个明显完整的逆转元件在几种谷类物种着丝粒区域的优先（或排他）定位，引发了关于其在核型进化和着丝粒功能中作用的有趣问题。
