Rapid generation of long tandem DNA repeat arrays by homologous recombination in yeast to study their function in mammalian genomes

Tandem repeats, also referred to as satellite DNA, represent a major class of repetitive DNA, whose function in the shaping of the human genome is only beginning to be explored. These repetitive sequences can be located in exons, introns, or intergenic regions, and their polymorphisms provide a unique source of genomic variability. Recent evidence also suggests that the repeat variants can influence the expression of entire loci and disease susceptibility [1,2]. Satellite sequences vary both in their repeat unit size and in their array length. Microsatellites are the smallest, with a repeat size of as little as few base pairs. The expansions of microsatellites associated with diseases have been referred to as dynamic mutations. Another class of repeat sequences is the classic satellites. They are much more abundant in the mammalian genome and consist of larger size repeat units ranging from 20-30 base pairs to a few kilobases. The array size of classic satellites may exceed several megabases.The most commonly known regions enriched by classic satellites are centromeric and pericentromeric regions. In mammals and other multicellular eukaryotes, these regions are characterized by very large arrays of different tandem repeated DNA sequences. Although centromeric DNA repeat sequences are thought to be structurally and/or functionally important for forming a functional kinetochore, they are poorly conserved between species. For example, mouse chromosomes have two types of DNA repeat sequences, the major satellite repeat (~6 Mb array/234 bp per repeat unit) and the minor satellite repeat (~600 kb array/120 bp per repeat unit) [3,4]. The major mouse satellite is found in the pericentromeric region, and the minor mouse satellite is found in the centric constriction of the centromere [3,5]. The centromeres of human chromosomes are characterized by the presence of megabase-size alpha-satellite DNA arrays (also known as alphoid DNA), which are composed of a tandem array of a 1