EFFECT OF NUCLEAR-PROTEIN HMG1 ON IN-VITRO SLIPPAGE SYNTHESIS OF THE TANDEM REPEAT DTG-CENTER-DOT-DCA

Tandem repeats of simple doubler and tripler sequences occur with high frequency in the DNA of eucaryotes. Among the most frequent is the re peat of dTG, which has unusual structural properties. We show here tha t HMG 1 (modeled by the second HMG box motif from HMG1 of the rat, HMG b) binds to complexes formed from annealing unequal lengths of dTG.dCA and inhibits the in vitro elongation of these complexes by the Klenow fragment of DNA polymerase I at 37 degrees C. At 46 degrees C, HMGb e nhances the elongation. Polylysine inhibits elongation at both tempera tures. These results show that the stability of this repeat in vivo ca n be influenced by the presence of basic proteins in general, and more selectively by the abundant nuclear protein HMG1.