Fu H, Park W, Yan X, Zheng Z, Shen B, Dooner H K
The Waksman Institute, Rutgers University, Piscataway, NJ 08855, USA.
Proc Natl Acad Sci U S A. 2001 Jul 17;98(15):8903-8. doi: 10.1073/pnas.141221898. Epub 2001 Jul 3.
The bronze (bz) locus exhibits the highest rate of recombination of any gene in higher plants. To investigate the possible basis of this high rate of recombination, we have analyzed the physical organization of the region around the bz locus. Two adjacent bacterial artificial chromosome clones, comprising a 240-kb contig centered around the Bz-McC allele, were isolated, and 60 kb of contiguous DNA spanning the two bacterial artificial chromosome clones was sequenced. We find that the bz locus lies in an unusually gene-rich region of the maize genome. Ten genes, at least eight of which are shown to be transcribed, are contained in a 32-kb stretch of DNA that is uninterrupted by retrotransposons. We have isolated nearly full length cDNAs corresponding to the five proximal genes in the cluster. The average intertranscript distance between them is just 1 kb, revealing a surprisingly compact packaging of adjacent genes in this part of the genome. At least 11 small insertions, including several previously described miniature inverted repeat transposable elements, were detected in the introns and 3' untranslated regions of genes and between genes. The gene-rich region is flanked at the proximal and distal ends by retrotransposon blocks. Thus, the maize genome appears to have scattered regions of high gene density similar to those found in other plants. The unusually high rate of intragenic recombination seen in bz may be related to the very high gene density of the region.
青铜色（bz）基因座在高等植物中表现出任何基因中最高的重组率。为了研究这种高重组率的可能基础，我们分析了bz基因座周围区域的物理组织。分离出两个相邻的细菌人工染色体克隆，它们包含以Bz-McC等位基因为中心的240 kb重叠群，并对跨越这两个细菌人工染色体克隆的60 kb连续DNA进行了测序。我们发现bz基因座位于玉米基因组中一个异常富含基因的区域。在一段32 kb的DNA片段中包含10个基因，其中至少8个基因被证明是转录的，该片段未被逆转座子打断。我们已经分离出与该簇中五个近端基因相对应的几乎全长的cDNA。它们之间的平均转录本间距仅为1 kb，这揭示了基因组这一部分中相邻基因令人惊讶的紧密包装。在基因的内含子和3'非翻译区以及基因之间检测到至少11个小插入，包括几个先前描述的微型反向重复转座元件。富含基因的区域在近端和远端两侧都有逆转座子块。因此，玉米基因组似乎有与其他植物中发现的类似的高基因密度分散区域。在bz中观察到的异常高的基因内重组率可能与该区域非常高的基因密度有关。
