Dooner H K, Martínez-Férez I M
Waksman Institute, Rutgers University, Piscataway, New Jersey 08855, USA.
Plant Cell. 1997 Sep;9(9):1633-46. doi: 10.1105/tpc.9.9.1633.
The bronze (bz) gene is a recombinational hotspot in the maize genome: its level of meiotic recombination per unit of physical length is > 100-fold higher than the genome's average and is the highest of any plant gene analyzed to date. Here, we examine whether recombination is also unevenly distributed within the bz gene. In yeast genes, recombination (conversion) is polarized, being higher at the end of the gene where recombination is presumably initiated. We have analyzed products of meiotic recombination between heteroallelic pairs of bz mutations in both the presence and absence of heterologies and have sequenced the recombination junction in 130 such Bz intragenic recombinants. We have found that in the absence of heterologies, recombination is proportional to physical distance across the bz gene. The simplest interpretation for this lack of polarity is that recombination is initiated randomly within the gene. Insertion mutations affect the frequency and distribution of intragenic recombination events at bz, creating hotspots and coldspots. Single base pair heterologies also affect recombination, with fewer recombination events than expected by chance occurring in regions of the bz gene with a high density of heterologies. We also provide evidence that meiotic recombination in maize is conservative, that is, it does not introduce changes, and that meiotic conversion tracts are continuous and similar in size to those in yeast.
青铜（bz）基因是玉米基因组中的一个重组热点：其每单位物理长度的减数分裂重组水平比基因组平均水平高100倍以上，是迄今为止分析的所有植物基因中最高的。在这里，我们研究重组在bz基因内是否也分布不均。在酵母基因中，重组（转换）是极化的，在基因末端较高，推测重组在此处起始。我们分析了在存在和不存在异源序列的情况下，bz突变的异等位基因对之间减数分裂重组的产物，并对130个此类Bz基因内重组体的重组连接点进行了测序。我们发现，在不存在异源序列的情况下，重组与bz基因的物理距离成正比。对这种缺乏极性的最简单解释是重组在基因内随机起始。插入突变影响bz基因内重组事件的频率和分布，产生热点和冷点。单碱基对异源序列也影响重组，在bz基因中异源序列高密度区域发生的重组事件比预期的偶然情况少。我们还提供了证据表明玉米中的减数分裂重组是保守的，也就是说，它不会引入变化，并且减数分裂转换片段是连续的，大小与酵母中的相似。
