BARE-1, A COPIA-LIKE RETROELEMENT IN BARLEY (HORDEUM-VULGARE L)

Retroviruses and retrotransposons make up the broad class of retroelem ents replicating and transposing via reverse transcriptase. Retroeleme nts have recently been found to be ubiquitous in the plants. We report here the isolation, sequence and analysis of a retroelement from barl ey (Hordeum vulgare L.) with all the features of a copia-like retrotra nsposon. This is named BARE-1 (for BArley RetroElement 1), the first s uch element described for barley. BARE-1 is 12 088 bp, with long termi nal repeats (LTRs) of 1829 bp containing perfect 6 bp inverted repeats at their ends and flanked by 4 bp direct repeats in the host DNA. Bet ween the long terminal repeats is an internal domain with a derived am ino acid sequence of 1285 residues, bearing homology to the gag, pro, int and rt domains of retroviruses and both plant and non-plant copia- like retrotransposons. Cultivated barley contains about 5000 elements in the genome similar to the BARE-1 putative gag domain, but ten-fold more hybridizing to rt or LTR probes. The particular BARE-1 element re ported here appears to be inactive, as the putative protein-coding dom ain is interrupted by four stop codons and a frameshift. In addition, the 3' LTR is 4% divergent from the 5' LTR and contains a 3135 bp inse rtion. Nevertheless, we have recently detected transcripts hybridizing to BARE-1 on northern blots, presumably from active copies. Analysis of BARE-1 expression and function in barley is currently underway.