De Souza C P, Ye X S, Osmani S A
Henry Hood Research Program, Weis Center for Research, Pennsylvania State University College of Medicine, Danville, Pennsylvania 17822, USA.
Mol Biol Cell. 1999 Nov;10(11):3661-74. doi: 10.1091/mbc.10.11.3661.
The G2 DNA damage and slowing of S-phase checkpoints over mitosis function through tyrosine phosphorylation of NIMX(cdc2) in Aspergillus nidulans. We demonstrate that breaking these checkpoints leads to a defective premature mitosis followed by dramatic rereplication of genomic DNA. Two additional checkpoint functions, uvsB and uvsD, also cause the rereplication phenotype after their mutation allows premature mitosis in the presence of low concentrations of hydroxyurea. uvsB is shown to encode a rad3/ATR homologue, whereas uvsD displays homology to rad26, which has only previously been identified in Schizosaccharomyces pombe. uvsB(rad3) and uvsD(rad26) have G2 checkpoint functions over mitosis and another function essential for surviving DNA damage. The rereplication phenotype is accompanied by lack of NIME(cyclinB), but ectopic expression of active nondegradable NIME(cyclinB) does not arrest DNA rereplication. DNA rereplication can also be induced in cells that enter mitosis prematurely because of lack of tyrosine phosphorylation of NIMX(cdc2) and impaired anaphase-promoting complex function. The data demonstrate that lack of checkpoint control over mitosis can secondarily cause defects in the checkpoint system that prevents DNA rereplication in the absence of mitosis. This defines a new mechanism by which endoreplication of DNA can be triggered and maintained in eukaryotic cells.
在构巢曲霉中，G2期DNA损伤和有丝分裂期间S期检查点的延缓通过NIMX（cdc2）的酪氨酸磷酸化发挥作用。我们证明，打破这些检查点会导致有缺陷的过早有丝分裂，随后基因组DNA会大量重新复制。另外两个检查点功能，uvsB和uvsD，在其突变允许在低浓度羟基脲存在下过早有丝分裂后，也会导致重新复制表型。uvsB被证明编码一种rad3/ATR同源物，而uvsD与rad26具有同源性，rad26此前仅在粟酒裂殖酵母中被鉴定出来。uvsB（rad3）和uvsD（rad26）在有丝分裂过程中具有G2检查点功能，以及对DNA损伤存活至关重要的另一种功能。重新复制表型伴随着NIME（周期蛋白B）的缺失，但活性不可降解的NIME（周期蛋白B）的异位表达并不能阻止DNA重新复制。DNA重新复制也可在因NIMX（cdc2）酪氨酸磷酸化缺乏和后期促进复合物功能受损而过早进入有丝分裂的细胞中诱导产生。数据表明，对有丝分裂缺乏检查点控制会继发导致在无有丝分裂时防止DNA重新复制的检查点系统出现缺陷。这定义了一种在真核细胞中触发和维持DNA核内复制的新机制。
