Prado F, Aguilera A
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Spain.
Genetics. 1995 Jan;139(1):109-23. doi: 10.1093/genetics/139.1.109.
We have constructed novel DNA substrates (one inverted and three direct repeats) based on the same 0.6-kb repeat sequence to study deletions and inversions in Saccharomyces cerevisiae. Spontaneous deletions occur six to eight times more frequently than inversions, irrespective of the distance between the repeats. This difference can be explained by the observation that deletion events can be mediated by a recombination mechanism that can initiate within the intervening sequence of the repeats. Spontaneous and double-strand break (DSB)-induced deletions occur as RAD52-dependent and RAD52-independent events. Those deletion events initiated through a DSB in the unique intervening sequence require the Rad1/Rad10 endonuclease only if the break is distantly located from the flanking DNA repeats. We propose that deletions can occur as three types of recombination events: the conservative RAD52-dependent reciprocal exchange and the nonconservative events, one-ended invasion crossover, and single-strand annealing (SSA). We suggest that one-ended invasion is RAD52 dependent, whereas SSA is RAD52 independent. Whereas deletions, like inversions, occur through reciprocal exchange, deletions can also occur through SSA or one-ended invasion. We propose that the contribution of reciprocal exchange and one-ended invasion crossover vs. SSA events to overall spontaneous deletions is a feature specific for each repeat system, determined by the initiation event and the availability of the Rad52 protein. We discuss the role of the Rad1/Rad10 endonuclease on the initial steps of one-ended invasion crossover and SSA as a function of the location of the initiation event relative to the repeats. We also show that the frequency of recombination between repeats is the same independent of their location (whether on circular plasmids, linear minichromosomes, or natural chromosomes) and have similar RAD52 dependence.
我们构建了基于相同0.6kb重复序列的新型DNA底物（一个反向重复和三个正向重复），以研究酿酒酵母中的缺失和倒位。自发缺失的发生频率比倒位高六到八倍，与重复序列之间的距离无关。这种差异可以通过以下观察结果来解释：缺失事件可以由一种能在重复序列的间隔序列内起始的重组机制介导。自发和双链断裂（DSB）诱导的缺失以依赖RAD52和不依赖RAD52的事件形式发生。那些通过独特间隔序列中的DSB起始的缺失事件，只有当断裂远离侧翼DNA重复序列时才需要Rad1/Rad10核酸内切酶。我们提出缺失可以作为三种类型的重组事件发生：保守的依赖RAD52的相互交换以及非保守事件、单端侵入交叉和单链退火（SSA）。我们认为单端侵入依赖RAD52，而SSA不依赖RAD52。虽然缺失和倒位一样通过相互交换发生，但缺失也可以通过SSA或单端侵入发生。我们提出相互交换和单端侵入交叉与SSA事件对总体自发缺失的贡献是每个重复系统特有的特征，由起始事件和Rad52蛋白的可用性决定。我们讨论了Rad1/Rad10核酸内切酶在单端侵入交叉和SSA初始步骤中的作用，这是起始事件相对于重复序列位置的函数。我们还表明，重复序列之间的重组频率与其位置无关（无论位于环状质粒、线性微型染色体还是天然染色体上），并且具有相似的RAD52依赖性。
