Journal of Neuroscience, Vol 16, 1511-1522, Copyright © 1996 by Society for Neuroscience
Defects in courtship and vision caused by amino acid substitutions in a putative RNA-binding protein encoded by the no-on-transient A (nonA) gene of Drosophila
KG Rendahl, N Gaukhshteyn, DA Wheeler, TA Fry and JC Hall
Department of Biology, Brandeis University, Waltham, Massachusetts 02254, USA.
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.