We have identified the cyclin domain-containing proteins encoded by the genomes of 17 species of Aspergillus as well as 15 members of other genera of filamentous ascomycetes. Phylogenetic analyses reveal that the cyclins fall into three groups, as in other eukaryotic phyla, and, more significantly, that they are remarkably conserved in these fungi. All 32 species examined, for example, have three group I cyclins, cyclins that are particularly important because they regulate the cell cycle, and these are highly conserved. Within the group I cyclins there are three distinct clades, and each fungus has a single member of each clade. These findings are in marked contrast to the yeasts Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Candida albicans, which have more numerous group I cyclins. These results indicate that findings on cyclin function made with a model Aspergillus species, such as A. nidulans, are likely to apply to other Aspergilli and be informative for a broad range of filamentous ascomycetes. In this regard, we note that the functions of only one Aspergillus group I cyclin have been analysed (NimE^{Cyclin B} of A. nidulans). We have consequently carried out an analysis of the members of the other two clades using A. nidulans as our model. We have found that one of these cyclins, PucA, is essential, but deletion of PucA in a strain carrying a deletion of CdhA, an activator of the anaphase promoting complex/cyclosome (APC/C), is not lethal. These data, coupled with data from heterokaryon rescue experiments, indicate that PucA is an essential G₁/S cyclin that is required for the inactivation of the APC/C-CdhA, which, in turn, allows the initiation of the S phase of the cell cycle. Our data also reveal that PucA has additional, non-essential, roles in the cell cycle in interphase. The A. nidulans member of the third clade (AN2137) has not previously been named or analyzed. We designate this gene clbA. ClbA localizes to kinetochores from mid G₂ until just prior to chromosomal condensation. Deletion of clbA does not affect viability. However, by using a regulatable promoter system new to Aspergillus, we have found that expression of a version of ClbA in which the destruction box sequences have been removed is lethal and causes a mitotic arrest and a high frequency of non-disjunction. Thus, although ClbA is not essential, its timely destruction is essential for viability, chromosomal disjunction, and successful completion of mitosis.

我们已经鉴定出由 17 个曲霉属以及其他丝状子囊菌属的 15 个成员的基因组编码的含有细胞周期蛋白结构域的蛋白质。系统发育分析表明，与其他真核生物门一样，细胞周期蛋白分为三类，更重要的是，它们在这些真菌中非常保守。例如，所检查的所有 32 个物种都具有三种 I 类细胞周期蛋白，这些细胞周期蛋白特别重要，因为它们调节细胞周期，而且高度保守。在 I 类细胞周期蛋白中，存在三个不同的进化枝，并且每种真菌在每个进化枝中都有一个成员。这些发现与酿酒酵母、粟酒裂殖酵母和白色念珠菌形成鲜明对比，后者具有更多的 I 类细胞周期蛋白。这些结果表明，用模型曲霉属物种（例如构巢曲霉）得出的细胞周期蛋白功能的发现可能适用于其他曲霉，并为广泛的丝状子囊菌提供信息。在这方面，我们注意到仅分析了一种曲霉菌I 组细胞周期蛋白（构巢曲霉的NimE^{细胞周期蛋白 B}）的功能。因此，我们使用构巢曲霉作为模型对其他两个分支的成员进行了分析。我们发现这些细胞周期蛋白之一 PucA 是必需的，但在携带 CdhA（后期促进复合物/细胞周期体 (APC/C) 激活剂）缺失的菌株中 PucA 的缺失并不致命。这些数据与异核拯救实验的数据相结合，表明 PucA 是一种重要的 G ₁ /S 细胞周期蛋白，是 APC/C-CdhA 失活所必需的，而 APC/C-CdhA 反过来又允许启动细胞周期的 S 期。细胞周期。我们的数据还表明，PucA 在细胞周期的间期中具有额外的、非必需的作用。第三进化枝的构巢构巢菌成员(AN2137) 此前尚未被命名或分析。我们将该基因命名为clbA。_{ClbA 从 G 2}中期直到染色体凝缩之前定位于动粒。删除clbA不会影响活力。然而，通过使用曲霉属新的可调节启动子系统，我们发现破坏盒序列被去除的 ClbA 版本的表达是致命的，并导致有丝分裂停滞和高频率的不分裂。因此，尽管 ClbA 不是必需的，但它的及时破坏对于活力、染色体分离和有丝分裂的成功完成至关重要。