Diversity in a chorion multigene family created by tandem duplications and a putative gene-conversion event

Abstract

Two families of high-cysteine chorion proteins in Bombyx mori are encoded in 15 tandemly arranged nonidentical gene pairs. It is assumed that this locus arose by duplication with subsequent sequence divergence. We have compared DNA sequences from two such neighboring pairs of genes in an attempt to understand the manner in which diversity has been generated and/or removed. A high level of sequence identity (91%-99%) was found between the repeats throughout the transcribed and flanking regions, with two significant exceptions. First, in the DNA segment encoding a conserved region of the chorion proteins, ten substitutions were detected in a 39-base-pair region. This localized region of high variability would suggest an intergene conversion-like event. Second, a length difference of 141 base pairs was detected in a region encoding the carboxy-terminal arm of the protein. This difference can be explained by three separate reiterations of single codons (3 base pairs) separated in time by duplication or triplication events.