ENHANCED TRANSCRIPTION FACTOR ACCESS TO ARRAYS OF HISTONE H3 H4 TETRAMER-CENTER-DOT-DNA COMPLEXES IN-VITRO - IMPLICATIONS FOR REPLICATION AND TRANSCRIPTION/

Defined model systems consisting of physiologically spaced arrays of H 3/H4 tetramer.5S rDNA complexes have been assembled in vitro from pure components. Analytical hydrodynamic and electrophoretic studies have revealed that the structural features of H3/H4 tetramer arrays closely resemble those of naked DNA, The reptation in agarose gels of H3/H4 t etramer arrays is essentially indistinguishable from naked DNA, the ge l-free mobility of H3/H4 tetramer arrays relative to naked DNA is redu ced by only 6% compared with 20% for nucleosomal arrays, and H3/H4 tet ramer arrays are incapable of folding under ionic conditions where nuc leosomal arrays are extensively folded. We further show that the cogna te binding sites for transcription factor TFIIIA are significantly mor e accessible when the rDNA is complexed with H3/H4 tetramers than with histone octamers. These results suggest that the processes of DNA rep lication and transcription have evolved to exploit the unique structur al properties of H3/H4 tetramer arrays.