Franklin Amie E, Golubovskaya Inna N, Bass Hank W, Cande W Zacheus
Department of Molecular and Cell Biology, 345 Life Sciences Addition, University of California at Berkeley, CA 94720, Berkeley, USA.
Chromosoma. 2003 Jul;112(1):17-25. doi: 10.1007/s00412-003-0242-8. Epub 2003 Jun 14.
The RecA homolog, RAD51, performs a central role in catalyzing the DNA strand exchange event of meiotic recombination. During meiosis, RAD51 complexes develop on pairing chromosomes and then most disappear upon synapsis. In the maize meiotic mutant desynaptic2 (dsy2), homologous chromosome pairing and recombination are reduced by ~70% in male meiosis. Fluorescent in situ hybridization studies demonstrate that a normal telomere bouquet develops but the pairing of a representative gene locus is still only 25%. Chromosome synapsis is aberrant as exemplified by unsynapsed regions of the chromosomes. In the mutant, we observed unusual RAD51 structures during chromosome pairing. Instead of spherical single and double RAD51 structures, we saw long thin filaments that extended along or around a single chromosome or stretched between two widely separated chromosomes. Mapping with simple sequence repeat (SSR) markers places the dsy2 gene to near the centromere on chromosome 5, therefore it is not an allele of rad51. Thus, the normal dsy2 gene product is required for both homologous chromosome synapsis and proper RAD51 filament behavior when chromosomes pair.
RecA 同源物 RAD51 在催化减数分裂重组的 DNA 链交换事件中发挥核心作用。在减数分裂过程中，RAD51 复合体在配对染色体上形成，然后在联会时大部分消失。在玉米减数分裂突变体 desynaptic2（dsy2）中，雄性减数分裂中同源染色体配对和重组减少了约 70%。荧光原位杂交研究表明，正常的端粒花束形成，但一个代表性基因座的配对率仍仅为 25%。染色体联会异常，如染色体的未联会区域所示。在突变体中，我们在染色体配对过程中观察到了异常的 RAD51 结构。我们看到的不是球形的单 RAD51 和双 RAD51 结构，而是沿着或围绕单个染色体延伸或在两个相距很远的染色体之间伸展的细长丝。用简单序列重复（SSR）标记进行定位将 dsy2 基因定位到 5 号染色体着丝粒附近，因此它不是 rad51 的等位基因。因此，正常的 dsy2 基因产物对于同源染色体联会以及染色体配对时 RAD51 丝的正常行为都是必需的。
