Molecular variation of the testes-specific βNACtes genes in the Drosophila melanogaster genome

Abstract

The βNACtes gene family of the Drosophila melanogaster genome provides a model for investigating the mechanisms of the molecular evolution of recently evolved genes. The βNACtes genes code for proteins that are homologous to the subunit of the nascent polypeptide-associated complex (NAC), are expressed exclusively in the testis, and are localized on the X chromosome as two-gene clusters and one separate copy. Population polymorphism of the βNACtes genes was studied using several wild-type D. melanogaster stocks, and βNACtes paralogs were compared with each other. A heterogeneous pattern was observed for βNACtes polymorphism: the 3′ genes of the two-gene clusters were low polymorphic, whereas, separate, the βNACtes1 gene was the most variable. The 5′ βNACtes copies of the two-gene tandems were practically identical, whereas the 3′ βNACtes copies were highly diverged. Hence, local gene conversion was assumed to provide for the selective homogenization of the 5′ genes. A comparison of the βNACtes paralogs showed that the majority of amino acid differences were in the N-terminal region, containing the βNAC domain. The McDonald-Kreitman test was used to analyze the divergence of βNACtes paralogs and implicated positive selection in the evolution of the βNACtes gene family.