新的表現(xiàn)型在演化過程中是怎樣被引入而又不會(huì)失去適應(yīng)性的,，這個(gè)問題在分子層面上基本上仍未得到解釋,。在三種子囊菌酵母中對(duì)一個(gè)眾所周知的過程（交配類型的確定）的分子細(xì)節(jié)進(jìn)行比較的一系列實(shí)驗(yàn)，顯示了一個(gè)轉(zhuǎn)錄回路（一種新的調(diào)控因子的插入）的構(gòu)型所發(fā)生的一個(gè)演化上的變化,，這種變化保留了一種古老的調(diào)控形式,，但產(chǎn)生了一個(gè)重要的新表現(xiàn)型。這個(gè)新變種使得“奶酪酵母”（乳酸克魯維斯酵母）只有在養(yǎng)分短缺時(shí)才交配,，從而將食物供應(yīng)狀況也考慮了進(jìn)來,，這種行為在釀酒酵母或人類病原體白念珠菌中是不存在的。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09560
Intercalation of a new tier of transcription regulation into an ancient circuit
Lauren N. Booth,Brian B. Tuch& Alexander D. Johnson
Changes in gene regulatory networks are a major source of evolutionary novelty1, 2, 3. Here we describe a specific type of network rewiring event, one that intercalates a new level of transcriptional control into an ancient circuit. We deduce that, over evolutionary time, the direct ancestral connections between a regulator and its target genes were broken and replaced by indirect connections, preserving the overall logic of the ancestral circuit but producing a new behaviour. The example was uncovered through a series of experiments in three ascomycete yeasts: the bakers’ yeast Saccharomyces cerevisiae, the dairy yeast Kluyveromyces lactis and the human pathogen Candida albicans. All three species have three cell types: two mating-competent cell forms (a and α) and the product of their mating (a/α), which is mating-incompetent. In the ancestral mating circuit, two homeodomain proteins, Mata1 and Matα2, form a heterodimer that directly represses four genes that are expressed only in a and α cells and are required for mating4, 5, 6. In a relatively recent ancestor of K. lactis, a reorganization occurred. The Mata1–Matα2 heterodimer represses the same four genes (known as the core haploid-specific genes) but now does so indirectly through an intermediate regulatory protein, Rme1. The overall logic of the ancestral circuit is preserved (haploid-specific genes ON in a and α cells and OFF in a/α cells), but a new phenotype was produced by the rewiring: unlike S. cerevisiae and C. albicans, K. lactis integrates nutritional signals, by means of Rme1, into the decision of whether or not to mate.
