PAIRING OF DNA FRAGMENTS CONTAINING (GGA-TCC)(N) REPEATS AND PROMOTION BY HIGH-MOBILITY GROUP PROTEIN-1 AND HISTONE H1

Tandemly repealed DNA sequences of(GGA:TCC)(n) are found in tracts up to 50 base pairs long, dispersed at thousands of sites throughout the genomes of eukaryotes, Here we demonstrate the formation of complexes paired between two DNAs containing such repeats in vitro and show enha ncement of the pairing by glutathione S-transferase fusion proteins of high mobility group protein 1 and histone H1, This assembly depends o n incubation time at 37 degrees C and concentrations of the proteins a nd DNA, and the enhancement is inhibited by distamycin and actinomycin D interacting DNA through the minor groove, Structure of the DNA-DNA complex is deduced by comparison of its mobility in gel electrophoresi s with those of synthetic markers of heterotetramers. Three synthetic and genomic DNA fragments containing repeats that have different arran gements exhibit different efficiencies of DNA pairing, implying that t he pairing is affected by the number of repeat units and the arrangeme nt of repeats in a sequence, Intriguingly, pairing occurs between homo logous fragments but not between heterologous DNAs among the three, Th ese results suggest that the repeat-mediated DNA pairing plays a role in organization of higher order architecture of chromatin and possibly chromosome segregation requiring sequence-specific association events of DNA molecules.