加拿大蒙特利尔大学研究人员在生物体如何选择其交配伴侣的机理研究上取得重要进展。他们发现，一种分子开关在对某个潜在的交配对象的信号做出反应时，分子开关得以激活。分子开关的激活使生物体知道附近有一个健康的最佳交配候选对象，并做出交配决定。相关文章发表在最新出版的《自然》杂志上。

达尔文在150年前首次发现生物体如何选择和为什么选择的交配对象的行为原则。达尔文曾经详细解释了一头母狮为何会选择一头最强壮的雄狮进行交配，一只母孔雀为何会选择一只羽毛最美丽的公孔雀交配的原因。加拿大科学家使用酵母菌在分子水平上发现了与达尔文理论相同的交配对象选择原理。

加拿大蒙特利尔大学生化系教授斯蒂芬·米奇尼克介绍说，研究结果表明，交配的决定由一种简单的化学开关所控制，这种开关将收到的生物信息素信号转换成了细胞的反应。

他介绍，当生物信息素信号增强时，细胞中的两个生化酶开始互相竞争，其中一个得到加强，而另一个则会在代号为Ste5的蛋白质上移除一个化学修饰。在生物信息素信号达到关键的阀值时，生物酶中的一个经过竞争，其能力超过了另一个经过生物酶修饰Ste5蛋白质的能力，细胞就会收到一个即时的化学信息，该信息即是：交配时间到了。

研究中，科学家使用了一种单细胞生物体酵母菌作为对象。米奇尼克教授认为，虽然酵母菌与人体存在很大的不同，但是在分子和细胞水平却有许多相似之处。科学家在酵母菌中所发现的可开关的分子，与在人体细胞内发现的分子形式非常相似。

研究人员表示，使用酵母菌可以展示出细胞如何做出一个重要的决定。当酵母细胞决定要交配时，它们必须知道很靠近的地方存在一个交配对象，然后迅速做出准备交配的决定。研究发现，酵母细胞做出决定不仅快，而且非常精确。尽管附近有许多处于竞争状态的候选交配对象，它们仍然可以做出最佳的选择。

原文出处：

Nature doi:10.1038/nature08946

The scaffold protein Ste5 directly controls a switch-like mating decision in yeast
Mohan K. Malleshaiah1,6, Vahid Shahrezaei3,6, Peter S. Swain4,5 & Stephen W. Michnick1,2

1 Département de Biochimie,
2 Centre Robert-Cedergren, Bio-Informatique et Génomique Université de Montréal, C.P. 6128, Succursale centre-ville Montréal, Québec H3C 3J7, Canada
3 Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
4 Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montréal, Québec H3G 1Y6, Canada
5 Centre for Systems Biology at Edinburgh, University of Edinburgh, Edinburgh EH9 3JD, UK
6 These authors contributed equally to this work.

Evolution has resulted in numerous innovations that allow organisms to increase their fitness by choosing particular mating partners, including secondary sexual characteristics, behavioural patterns, chemical attractants and corresponding sensory mechanisms1. The haploid yeast Saccharomyces cerevisiae selects mating partners by interpreting the concentration gradient of pheromone secreted by potential mates through a network of mitogen-activated protein kinase (MAPK) signalling proteins2, 3. The mating decision in yeast is an all-or-none, or switch-like, response that allows cells to filter weak pheromone signals, thus avoiding inappropriate commitment to mating by responding only at or above critical concentrations when a mate is sufficiently close4. The molecular mechanisms that govern the switch-like mating decision are poorly understood. Here we show that the switching mechanism arises from competition between the MAPK Fus3 and a phosphatase Ptc1 for control of the phosphorylation state of four sites on the scaffold protein Ste5. This competition results in a switch-like dissociation of Fus3 from Ste5 that is necessary to generate the switch-like mating response. Thus, the decision to mate is made at an early stage in the pheromone pathway and occurs rapidly, perhaps to prevent the loss of the potential mate to competitors. We argue that the architecture of the Fus3–Ste5–Ptc1 circuit generates a novel ultrasensitivity mechanism, which is robust to variations in the concentrations of these proteins. This robustness helps assure that mating can occur despite stochastic or genetic variation between individuals. The role of Ste5 as a direct modulator of a cell-fate decision expands the functional repertoire of scaffold proteins beyond providing specificity and efficiency of information processing5, 6. Similar mechanisms may govern cellular decisions in higher organisms and be disrupted in cancer.