Genomic organization, evolution, and structural peculiarities of highly repetitive DNA of Hordeum vulgare

A fraction of highly repeated DNA sequences of Hordeum vulgare has been investigated by cloning 19 separate highly repetitive sequences in the plasmid pBR327. Characteristics studied included genus specificity of isolated sequences, their prevalence, and genome organization. Sequences (pHv7161, pHv7191, pHv7179) have been identified that are the most widespread in the H. vulgare genome and have a complicated arrangement. A tandemly arranged sequence, pHv7141, was also identified. The primary structure of a 999 bp long, BamHI fragment of one of the most widespread sequences, pHv7161, as well as the adjacent pHv7302 and pHv7245 sequences was determined. The fragment abounds in inverted repeats, of which two are flanked by direct repeats, and contains short subrepeats, A, B, and C, and a great variety of potential protein-binding sites. A comparison is drawn between the content and genome organization of highly repeated DNA sequences of H. vulgare and those of the wild barley species Hordeum bulbosum, Hordeum jubatum, Hordeum geniculatum, Hordeum brevisubulatum, Hordeum turkestanicum, and Hordeum murinum. According to the above characters (close copy number and genome organization similarity of highly repetitive sequences) the species under discussion have been classified into four groups. This division is in good agreement with other data on interspecific crossing in Hordeum and on chromosome pairing in hybrid meiosis.