SILK MOTH CHORION PSEUDOGENES - HALLMARKS OF GENOMIC EVOLUTION BY SEQUENCE DUPLICATION AND GENE CONVERSION

The part of the genetic locus of the domesticated silk moth, Bombyx mo ri, in which high cysteine (Hc) chorion genes of late developmental sp ecificity reside contains regions encompassing genelike sequences whic h exhibit properties distinct from those of functional Hc genes. One o f these regions has been characterized and shown to contain a chorion pseudogene, psiHcB.15, which shares pronounced similarities with a tra nscribed chorion pseudogene, psiHcB. 12/13, which was characterized pr eviously. Both pseudogenes are homologous to HcB chorion genes but bea r multiple single nucleotide substitutions and short segmental mutatio ns (insertions and deletions) which introduce translational frame shif ts and termination codons in the coding regions. Structural characteri stics unique to the two pseudogenes suggest that psiHcB. 15 was genera ted first from a functional HcB gene and gave rise subsequently to psi HcB 12/13 as a result of a sequence duplication event. The two pseudog enes can be distinguished from each other by the presence of distinct regions of similarity to the consensus sequence of functional HcB gene s which appear to have arisen from gene-conversion-mediated correction al events. These findings lend support to the hypothesis that chorion pseudogene sequences represent reservoirs of genetic information that participates in the evolution of the chorion locus rather than relics of inactivated genes passively awaiting extinction.