A novel AT-rich tandem repeat of Brassica nigra

A family of repeated DNA sequences present in the genome of Brassica nigra has been characterized by cloning and sequencing of the repeat element. It is a novel tandem repeat, different from any other known plant repetitive DNA sequences. The monomeric unit is 348 bp in length and highly AT-rich (74%) as compared to other reported plant tandem repeated DNA sequences. The average copy number of the cloned repeat is 1 × 10 5 per haploid genome and constitutes approximately 2.5% of the total B. nigra genome. It shows no sequence homology with the 177 bp satellite DNA sequences of other crucifers as well as with other plant tandem repeated DNA. The distribution and evolution of this tandem repeat in crucifers is discussed.