Genomic simple repetitive DNAs are targets for differential binding of nuclear proteins

The biological meaning of abundant simple repetitive DNA sequences in eukaryote genomes is obscure. Therefore, (GAA)n, (GT)n, and composite (GT)n(GA)m, blocks were characterized for protein binding in the repeat and flanking sequences of cloned genomic DNA fragments. In gel mobility shift and competition assays the binding of nuclear proteins to the repeats was specific (including some flanking single copy sequences). DNase footprinting revealed the target sequences within and adjacent to the repeats. Chemical modifications (OsO4, DEPC) demonstrated non-B DNA structures in the polypurine blocks. The binding of nuclear proteins in and around simple repeat sequences refute biological insignificance of all of these ubiquitously interspersed elements.