CLONING AND CHARACTERIZATION OF A HIGHLY REPEATED DNA-SEQUENCE IN HORDEUM-VULGARE L

A novel repetitive DNA sequence, R10hvcop. has been identified in the barley (Hordeum vulgare L.) genome. This 830 base pair (bp) DNA sequen ce has a 606-bp open reading frame and is present as approximately 1.9 6 x 10(5) copies per haploid barley genome. Southern blot analysis rev ealed that repetitive DNA elements containing R10hvcop and related seq uences were dispersed within the barley chromosomes. Sequences similar to R10hvcop were also found in wheat (Triticum aestivum L.), rye (Sec ale cereale L.), and oat (Avena sativa L.) with copy numbers of 8 x 10 (4), 1.39 x 10(5), and 7.9 x 10(4) per haploid genome, respectively. S equences similar to R10hvcop were also present in the corn (Zen mays L . ssp. mays) genome, but they were not highly repeated. Barley, wheat, rye, oat, and corn showed species-specific restriction fragment lengt h polymorphisms of R10hvcop and related sequences. Computer-based simi larity searches revealed that R10hvcop is closely related to reverse t ranscriptase genes in retrotransposons and retrotransposon-like elemen ts of several giant species and of Drosophila. The highly repetitive n ature, interspersed distribution, and high degree of similarity to rev erse transcriptase genes suggests that R10hvcop contains the sequence of a diverged reverse transcriptase gene.