RETROTRANSPOSONS IN THE FLANKING REGIONS OF NORMAL PLANT GENES - A ROLE FOR COPIA-LIKE ELEMENTS IN THE EVOLUTION OF GENE STRUCTURE AND EXPRESSION

The wx-K mutation results from the insertion of copia-like retrotransp oson into exon 12 of the maize waxy gene, This retrotransposon, named Hopscotch, has one long open reading frame encoding all of the domains required for transposition. Computer-assisted database searches using Hopscotch and other plant copia-like retroelements as query sequences have revealed that ancient, degenerate retrotransposon insertions are found in close proximity to 21 previously sequenced plant genes. The data suggest that these elements may be involved in gene duplication a nd the regulation of gene expression. Similar searches using the Droso phila retrotransposon copia did not reveal any retrotransposon-like se quences in the flanking regions of animal genes. These results, togeth er with the recent finding that reverse-transcriptase sequences charac teristic of copia-like elements are ubiquitous and diverse in plants, suggest that copia-like retrotransposons are an ancient component of p lant genomes.