Nucleotide variation at the no-on-transient A gene in Drosophila littoralis

The no-on-transient A (nonA) gene encodes a putative RNA-binding protein, and mutations in this gene are known to affect vision, male courtship song and viability in Drosophila melanogaster. Here we have sequenced the coding region of the nonA gene of Drosophila littoralis and compared it with those of Drosophila virilis and D. melanogaster. All portions of nonA appeared to be conserved between D. littoralis and D. virilis, while the 5' region of the gene of these two species showed high divergence from that of a more distantly-related species, D. melanogaster. The same was true for the glycine repeat regions. No significant deviation from neutrality was observed in the analysis of intraspecific nucleotide variation in 5' or 3' region of the nonA gene in D. littoralis population. Also, comparison of D. littoralis sequences with homologous sequence of D. virilis suggests that the gene is evolving neutrally in D. virilis group. Divergence of the 5' regions between D. virilis group species and D. melanogaster could be a result of positive selection, but this finding is obscured by the long divergence time of the species groups.