Benitez T, Nurse P, Mitchison J M
J Cell Sci. 1980 Dec;46:399-431. doi: 10.1242/jcs.46.1.399.
The induction potentials of 2 enzymes, sucrase and arginase, have been measured in asynchronous and synchronous cultures of the fission yeast Schizosaccharomyces pombe. The effect on potential of inhibiting DNA synthesis is asynchronous cultures has been studied using 2 temperature-sensitive dcd mutants, one blocked in DNA replication and the other blocked in mitosis. The results show that despite inhibition of DNA synthesis, sucrase and arginase potential both continue to increase exponentially for at least a generation of growth after shifting the cdc mutants from the permissive to the restrictive temperature. A second method of inhibiting DNA synthesis, using deoxyadenosine, has also been tested. Cells treated with deoxyadenosine stop the increase in potential for a short period. However, experiments carried out using a cdc mutant together with deoxyadenosine show that the block to the increase in potential is due to a side effect of the inhibitor. It appears that increase in potential is not dependent upon continued DNA replication, and that gene dosage does not control potential in the normal cell cycle. This conclusion is supported by measurements on mutants of different cell sizes. potential is proportional to size (protein content per cell is asynchronous culture) and not to DNA content. Although potential is not gene limited in normal cells, it does appear to be so in the abnormally large cells produced by a cdc block. If cdc mutants of different sizes are grown asynchronously, and DNA synthesis is inhibited by a shift to the restrictive temperature, there is no increase in potential. This critical ratio is different for the 2 enzymes, but for each enzyme it is similar in all the mutants tested. When large cells (produced by a mutant block for 4.5 h) are shifted down in temperature, there are synchronous rounds of DNA synthesis and division and also step doublings in potential. In synchronous cultures of wild type cells, both enzymes show a stepwise doubling of potential at 0.2 of a cycle after DNA replication. In synchronous cultures of cdc mutants blocked either in replication or in mitosis, the potential steps continue with the normal timing observed in wild type cells. This shows that the steps are not dependent on the events of the DNA-division cycle but are controlled by another mechanism. Attainment of a critical size might be part of this mechanism, but tests with size mutants argue against this.
在裂殖酵母粟酒裂殖酵母的异步和同步培养物中，已测量了两种酶（蔗糖酶和精氨酸酶）的诱导电位。使用两个温度敏感的cdc突变体研究了抑制异步培养物中DNA合成对电位的影响，其中一个突变体在DNA复制中受阻，另一个在有丝分裂中受阻。结果表明，尽管DNA合成受到抑制，但在将cdc突变体从允许温度转移到限制温度后，蔗糖酶和精氨酸酶的电位在至少一代生长过程中仍继续呈指数增加。还测试了另一种抑制DNA合成的方法，即使用脱氧腺苷。用脱氧腺苷处理的细胞在短时间内停止电位增加。然而，使用cdc突变体与脱氧腺苷一起进行的实验表明，电位增加受阻是由于抑制剂的副作用。似乎电位增加不依赖于持续的DNA复制，并且基因剂量在正常细胞周期中不控制电位。这一结论得到了对不同细胞大小的突变体测量结果的支持。电位与大小成正比（异步培养物中每个细胞的蛋白质含量），而与DNA含量无关。尽管在正常细胞中电位不受基因限制，但在由cdc阻断产生的异常大细胞中似乎是这样。如果不同大小的cdc突变体异步生长，并且通过转移到限制温度来抑制DNA合成，则电位不会增加。这两种酶的临界比率不同，但对于每种酶，在所有测试的突变体中都是相似的。当大细胞（由突变体阻断4.5小时产生）温度降低时，会有同步的DNA合成和分裂轮次，并且电位也会有阶梯式加倍。在野生型细胞的同步培养物中，两种酶在DNA复制后0.2个周期时电位都有阶梯式加倍。在复制或有丝分裂中受阻的cdc突变体的同步培养物中，电位阶梯以在野生型细胞中观察到的正常时间继续。这表明这些阶梯不依赖于DNA分裂周期的事件，而是由另一种机制控制。达到临界大小可能是这种机制的一部分，但对大小突变体的测试对此提出了反对。
