Advanced Genetic Sciences, 6701 San Pablo Avenue, Oakland, California 94608.
Genetics. 1986 Aug;113(4):1021-36. doi: 10.1093/genetics/113.4.1021.
The bronze (bz) locus in maize, located in the short arm of chromosome 9 (9S), is the structural gene for the anthocyanin biosynthetic enzyme UFGT. The gene has been cloned and its physical map has been oriented relative to the centromere of 9S. We report here the genetic fine structure mapping of several biochemically characterized EMS-induced bz-E mutations, derived from the Bz-W22 isoallele, and Ds insertion bz-m mutations, derived from the Bz-McC isoallele. Two UFGT(-), CRM(+ ) mutants (bz-E2 and bz-E5), which genetically identify coding sequences in the gene, and three UFGT(-), CRM(- )bz-E mutants were mapped against the Ds insertion mutants bz-m1 and bz-m2(DI) by selecting Bz intragenic recombinants from heterozygotes of the type bz-E/bz-m . The exclusive occurrence of one recombinant outside marker class allowed the unambiguous placement of the mutants in a genetic fine structure map. Peculiarly, the two CRM(+)bz-E mutants lie upstream of the three CRM(-)bz-E mutants and at a considerable genetic distance. The UFGT allozymes encoded by the progenitor alleles Bz-W22 and Bz-McC differ in two properties, thermal stability and activity. The sites responsible for these properties were mapped as unselected markers among the Bz intragenic recombinants. The thermal stability site, which also identifies a coding region of the gene, mapped very close to the CRM(+)bz-E mutant sites. The site responsible for variation in activity, which probably identifies a region involved in regulation of expression of the bz locus, mapped at the 5' or proximal end of the locus. It was found to be inseparable from the Ds insertion in bz-m1 that lies very close to the 5' end of the transcribed region.-Evidence was obtained that the insertion of Ds within the bz gene has a suppressing effect on intragenic recombination. Additional data are also presented supporting our observation that Ds affects the pattern of intragenic recombination at bz.-Based on the total genetic length of the bz gene and on the physical size of the transcribed region, we estimate that one unit of recombination at bronze corresponds to 14 kb of DNA. This estimate is more than 100 times smaller than the average value for the whole genome and implies that there may be regions, such as bronze, that serve as hotspots for recombination.
玉米 9 号染色体短臂上的青铜（bz）基因座是花色苷生物合成酶 UFGT 的结构基因。该基因已经被克隆，其物理图谱已经相对于 9S 的着丝粒定位。我们在这里报告了几个生物化学特征 EMS 诱导的 bz-E 突变的遗传精细结构作图，这些突变来自 Bz-W22 等位基因，以及 Ds 插入 bz-m 突变，来自 Bz-McC 等位基因。两个 UFGT(-), CRM(+ )突变体（bz-E2 和 bz-E5），在基因中鉴定出编码序列，以及三个 UFGT(-), CRM(- )bz-E 突变体通过从 bz-E/bz-m 的杂合体中选择 Bz 基因内重组体，被映射到 Ds 插入突变体 bz-m1 和 bz-m2(DI)上。唯一发生在一个重组体之外的标记类允许将突变体明确地放置在遗传精细结构图谱中。特别地，两个 CRM(+)bz-E 突变体位于三个 CRM(-)bz-E 突变体的上游，并且具有相当大的遗传距离。由亲本等位基因 Bz-W22 和 Bz-McC 编码的 UFGT 同工酶在热稳定性和活性方面存在两种差异。这些特性的位点被作为未选择的标记映射在 Bz 基因内重组体中。负责这些特性的位点映射到基因的编码区域附近，非常接近 CRM(+)bz-E 突变体的位点。负责活性变化的位点，可能鉴定出与 bz 基因表达调控有关的区域，映射到基因的 5'或近端端。发现 Ds 插入 bz-m1 中，这非常接近转录区域的 5'端，对基因内重组具有抑制作用。还提供了其他数据支持我们的观察结果，即 Ds 影响 bz 基因内重组的模式。基于 bz 基因的总遗传长度和转录区域的物理大小，我们估计青铜的一个重组单位对应于 14kb 的 DNA。这一估计值比整个基因组的平均值小 100 多倍，这意味着可能存在一些区域，如青铜，作为重组的热点。
