Poly[d(A.T)] and other synthetic polydeoxynucleotides containing oligoadenosine tracts form nucleosomes easily.
Synthetic double-stranded polydeoxynucleotides of the general form poly[d(AnT).d(ATn)], with n ranging from 3 to 11, have been synthesized. The conformation of the polymers was investigated by circular dichroism spectroscopy and the polymers were examined for their ability to form nucleosomes. Although spectra show that a circular dichroism band characteristic of poly[d(A.T)] appears in the polymer family for n greater than 7, we demonstrate that even polynucleotides with the longest tracts of contiguous adenosine bases (n = 11) are able to form nucleosomes when reconstituted using a histone exchange procedure. Thus resistance to nucleosome formation does not coincide with the appearance of features similar to that of poly[d(A.T)] over the bulk of the nucleosomal DNA. Furthermore, we show that an approximately 150 base-pair poly[d(A.T)] itself, long thought to be refractory to nucleosome formation, can assemble into such a protein-DNA complex when reconstituted by a low-salt exchange procedure. Competitive assays show that the homopolymer reconstitutes about as well as heterogeneous sequences DNA. Our work, therefore, suggests that highly adenosine-rich sequences in vivo apparently have a function that operates at a level other than that of nucleosome structure.
Puhl
H L
HL
Department of Chemistry, Lehigh University, Bethlehem, PA 18015.
Gudibande
S R
SR
Behe
M J
MJ
D001483:Base Sequence; D002499:Centrifugation, Density Gradient; D002942:Circular Dichroism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000648:ultrastructure*; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry; D011067:Poly dA-dT / Q000737:chemistry*; D011089:Polydeoxyribonucleotides / Q000737:chemistry*; D013329:Structure-Activity Relationship
D009707:Nucleosomes; D009838:Oligodeoxyribonucleotides; D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT