Rendahl K G, Gaukhshteyn N, Wheeler D A, Fry T A, Hall J C
Department of Biology, Brandeis University, Waltham, Massachusetts 02254, USA.
J Neurosci. 1996 Feb 15;16(4):1511-22. doi: 10.1523/JNEUROSCI.16-04-01511.1996.
The Drosophila no-on-transient A (nonA) gene is involved in the visual behaviors and courtship song of the fly. The NONA polypeptide contains two copies of the RNA-recognition motif (RRM), a hallmark of proteins involved in RNA binding, and an adjacent conserved charged region. This 311-amino-acid region is found in four other proteins and largely overlaps the Drosophila-Behavior/Human Splicing (or DBHS) domain. The newest family member, Drosophila nAhomo, was discovered in a database search, and encodes a protein with 80% identity to NONA. In this study, three nonA mutations generated by chemical mutagenesis were sequenced and found to fall within the conserved region. Site-directed mutagenesis of the two RRMs, and within a (conserved) charged region located C-terminal to them, was performed to determine the significance of these domains with respect to whole-organismal phenotypes. Behavior and viability were assessed in transformed flies, the genetic background of which lacks the nonA locus. Point mutations of amino acid 548 in the charged region confirmed the etiology of the nonAdiss courtship-song mutation and showed that a milder substitution at this site produced intermediate singing behavior, although it failed to rescue visual defects. Mutagenesis of the RRM1 domain resulted in effects on viability, vision, and courtship song. However, amino acid substitutions in RNP-II of RRM2 led to near-normal phenotypes, and the in vivo nonA mutations located in or near RRM2 caused visual defects only. Thus, we suggest that the first RRM could be important for all functions influenced by nonA, whereas the second RRM may be required primarily for normal vision.
果蝇无瞬时A（nonA）基因参与果蝇的视觉行为和求偶鸣叫。NONA多肽包含两个RNA识别基序（RRM）拷贝，这是参与RNA结合的蛋白质的一个标志，以及一个相邻的保守带电区域。这个由311个氨基酸组成的区域在其他四种蛋白质中也有发现，并且与果蝇行为/人类剪接（或DBHS）结构域有很大重叠。最新的家族成员果蝇nAhomo是在数据库搜索中发现的，它编码一种与NONA有80%同一性的蛋白质。在本研究中，对通过化学诱变产生的三个nonA突变进行了测序，发现它们位于保守区域内。对两个RRM以及它们C端的一个（保守）带电区域进行了定点诱变，以确定这些结构域对全生物体表型的重要性。在缺乏nonA基因座的遗传背景的转化果蝇中评估行为和活力。带电区域中氨基酸548的点突变证实了nonAdiss求偶鸣叫突变的病因，并且表明在该位点的一个较温和的替代产生了中间的鸣叫行为，尽管它未能挽救视觉缺陷。RRM1结构域的诱变导致对活力、视觉和求偶鸣叫的影响。然而，RRM2的RNP-II中的氨基酸替代导致接近正常的表型，并且位于RRM2内或附近的体内nonA突变仅导致视觉缺陷。因此，我们认为第一个RRM可能对nonA影响的所有功能都很重要，而第二个RRM可能主要是正常视觉所必需的。
