[Relationship between two distinct families of tandem repeats in rye heterochromatin]

BAC library constructed from the short arm of the first rye (Secale cereale L.) chromosome 1R was screened extensively in order to identify clones containing the copies of a tandemly organized repetitive DNA family, pSc200, which is the most abundant in the rye subtelomeric heterochromatin. Molecular organization of the monomers array and adjacent sequences have been studied in BAC 126/C20. The pSc200 array does not demonstrate the higher-order organization under treatment by different restrictases. The DNA adjacent to the pSc200 array consists of the different repeats included retrotransposon derivatives and another tandemly repeated XbaI family with monomer length of 576 bp, 475 of these show 82% similarity to part of the long terminal repeat of known retrotransposon Cereba. The sequencing of the 13 kb region in BAC 126/C20 revealed the direct junction of the pSc200 and XbaI monomers. The junction between these monomers was abrupt in the identical AT-rich site, CAAAAAT. Another recombinational signal is the palindromes in the close proximity to the site ofjunction. The presence of microhomologies promotes the efficiency action of the proteins involved in the mechanisms of double strand DNA break repair. To our knowledge, for the first time we revealed the direct junction of the monomers, which are longer than 100 bp length and belong to distinct families of tandem repeats from plant genomes.