Studies on synthetic chromatins containing poly(dA-dT) X poly(dA-dT) and poly(dG-dC) X poly(dG-dC).
Core histones (H2A,H2B,H3,H4)2, were reconstituted with the synthetic polynucleotides poly(dA-dT) X poly(dA-dT) and poly(dG-dC) X poly(dG-dC) to yield synthetic chromatins containing 200 basepairs per octamer. These synthetic chromatins displayed a 36% decrease in the circular dichroism (CD) peak ellipticity from the value of the polynucleotide free in solution; the poly(dA-dT) X poly(dA-dT)/chromatin showed an increase in the complexity of the thermal denaturation profile compared to that of the polynucleotide. Both the temperature of maximum dh/dT for each transition (Tm) and the relative amount of poly(dA-dT) X poly(dA-dT) in the synthetic chromatin melting in each of the four thermal transitions is a function of the ionic strength over the 0-5 mM sodium phosphate range (0.25 mM EDTA, pH 7.0); a shift of material toward higher melting transitions was observed with increasing ionic strength. The CD peak ellipticity value for both synthetic chromatins was ionic strength-independent over the 0-5 mM sodium phosphate range. These results are in contrast to those observed with H1/H5 stripped chicken erythrocyte chromatin (Fulmer, A. and Fasman, G.D. (1979) Biopolymers 18, 2875-2891), where an ionic strength dependence was found. Differences in the CD spectra between poly(dA-dT) X poly(dA-dT)/chromatin, poly(dG-dC) X poly(dG-dC)/chromatin and H1/H5 stripped chicken erythrocyte chromatin suggest subtle differences in assembly. Finally, the temperature dependence of the CD spectra of poly(dA-dT) X poly(dA-dT)-containing synthetic chromatin, which is similar to that for the polynucleotide, suggests the core histone bound polynucleotide has a large degree of conformational flexibility allowing it to undergo the premelt transition.
D000818:Animals; D002645:Chickens; D002843:Chromatin / Q000648:ultrastructure*; D002942:Circular Dichroism; D006657:Histones / Q000097:blood / Q000302:isolation & purification*; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet
D002843:Chromatin; D006657:Histones; D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT; C019530:poly(dC-dG)