Characterization of the stability and folding of H2A.Z chromatin particles- Implications for transcriptional activation

H2A.Z and H2A.1 nucleosome core particles and oligonucleosome arrays were o btained using recombinant versions of these histones and a native histone H 2B/H3/H4 complement reconstituted onto appropriate DNA templates. Analysis of the reconstituted nucleosome core particles using native polyacrylamide gel electrophoresis and DNase I footprinting showed that H2A.Z nucleosome c ore particles were almost structurally indistinguishable from its H2A.1 or native chicken erythrocyte counterparts. While this result is in good agree ment with the recently published crystallographic structure of the H2A.Z nu cleosome core particle (Suto, R. K., Clarkson, M J., Tremethick, D. J., and Luger, YL (2000) Nat. Struct. Biol. 7,1121-1124), the ionic strength depen dence of the sedimentation coefficient of these particles exhibits a substa ntial destabilization, which is most likely the result of the histone H2A.Z -H213 dimer binding less tightly to the nucleosome. Analytical ultracentrif uge analysis of the H2A.Z 208-12, a DNA template consisting of 12 tandem re peats of a 208-base pair sequence derived from the sea urchin Lytechinus va riegatus 5 S rRNA gene, reconstituted oligonucleosome complexes in the abse nce of histone HI shows that their NaCl-dependent folding ability is signif icantly reduced. These results support the notion that the histone H2A.Z va riant may play a chromatin-destabilizing role, which may be important for t ranscriptional activation.