Peixoto A A, Hennessy J M, Townson I, Hasan G, Rosbash M, Costa R, Kyriacou C P
Department of Genetics, University of Leicester, Leicester, LE1 7RH, United Kingdom.
Proc Natl Acad Sci U S A. 1998 Apr 14;95(8):4475-80. doi: 10.1073/pnas.95.8.4475.
The period (per) gene in Drosophila melanogaster provides an integral component of biological rhythmicity and encodes a protein that includes a repetitive threonine-glycine (Thr-Gly) tract. Similar repeats are found in the frq and wc2 clock genes of Neurospora crassa and in the mammalian per homologues, but their circadian functions are unknown. In Drosophilids, the length of the Thr-Gly repeat varies widely between species, and sequence comparisons have suggested that the repeat length coevolves with the immediately flanking amino acids. A functional test of the coevolution hypothesis was performed by generating several hybrid per transgenes between Drosophila pseudoobscura and D. melanogaster, whose repetitive regions differ in length by about 150 amino acids. The positions of the chimeric junctions were slightly altered in each transgene. Transformants carrying per constructs in which the repeat of one species was juxtaposed next to the flanking region of the other were almost arrhythmic or showed a striking temperature sensitivity of the circadian period. In contrast, transgenes in which the repeat and flanking regions were conspecific gave wild-type levels of circadian rescue. These results support the coevolutionary interpretation of the interspecific sequence changes in this region of the PER molecule and reveal a functional dimension to this process related to the clock's temperature compensation.
果蝇（Drosophila melanogaster）中的周期（per）基因是生物节律的一个重要组成部分，它编码一种包含重复苏氨酸 - 甘氨酸（Thr - Gly）序列的蛋白质。在粗糙脉孢菌（Neurospora crassa）的frq和wc2时钟基因以及哺乳动物的per同源物中也发现了类似的重复序列，但其昼夜节律功能尚不清楚。在果蝇类中，Thr - Gly重复序列的长度在不同物种间差异很大，序列比较表明重复序列长度与紧邻的氨基酸共同进化。通过在拟暗果蝇（Drosophila pseudoobscura）和黑腹果蝇（D. melanogaster）之间构建几个杂交per转基因进行了共同进化假说的功能测试，这两个物种的重复区域长度相差约150个氨基酸。每个转基因中嵌合连接点的位置略有改变。携带per构建体的转化体中，一个物种的重复序列与另一个物种的侧翼区域相邻，这些转化体几乎没有节律或表现出昼夜节律周期对温度的显著敏感性。相比之下，重复序列和侧翼区域为同种的转基因则能实现野生型水平的昼夜节律拯救。这些结果支持了对PER分子该区域种间序列变化的共同进化解释，并揭示了这一过程与时钟温度补偿相关的功能维度。
