ASSOCIATION OF POLY(CA)CENTER-DOT-POLY(TG) DNA FRAGMENTS INTO 4-STRANDED COMPLEXES BOUND BY HMG-1 AND HMG-2

The tandemly repeated DNA sequence poly(CA).poly(TG) is found in tract s up to 60 base pairs long, dispersed at thousands of sites throughout the genomes of eukaryotes. Double-stranded DNA fragments containing s uch sequences associated spontaneously with each other in vitro, in th e absence of protein, forming stable four-stranded structures that wer e detected by gel electrophoresis and electron microscopy. These struc tures were recognized specifically by the nuclear nonhistone high mobi lity group (HMG) proteins 1 and 2 as evidenced by gel retardation. Suc h sequence-specific complexes might be involved in vivo in recombinati on or other processes requiring specific association of two double-str anded DNA molecules.