EVOLUTION OF CHORION GENE FAMILIES IN LEPIDOPTERA - CHARACTERIZATION OF 15 CDNAS FROM THE GYPSY-MOTH

Fifteen unique chorion protein-encoding cDNAs from gypsy moth have bee n completely sequenced. These sequences are encoded by a family of gen es, based on pairwise similarity values of 78-100% within a 225-nt reg ion. Pairwise comparisons and maximum parsimony analysis strongly supp ort the existence of two clusters of 11 and four sequences each, calle d nod and noc2. While noc2 consists of two subclusters, there is littl e character support for subclusters within nod. The highly localized c haracter-state distribution on the parsimony tree in gypsy moth is rem iniscent of that in Bombyx mori, specifically for those chorion famili es that have been shown to undergo gene conversion. Gene conversion th us becomes a reasonable explanation for the homogeneity of nod sequenc es and for their distinctness from nod. The relationship between the t wo major clusters of chorion sequences in gypsy moth (noc1, noc2) and Bombyx mori (Bm alpha, Bm beta) has been addressed through mixed-speci es tree construction. All four groups cluster separately, thus providi ng no direct evidence of orthologous sequences. However, the occurrenc e of gene conversion could have eliminated such evidence. The relation ship between the chorion gene tree and the species cladogenic event is discussed, as are biases in codon usage, base composition, and nucleo tide transformations.