Experimental evidence for the role of domain swapping in the evolution of the histone fold.

The histone fold forms the fundamental endoskeleton of the protein core of the nucleosome and is also found in several transcription factors. We have investigated the evolutionary origins of this ubiquitous protein motif, which is found soluble exclusively as an antiparallel (handshake motif) dimer. We introduced a three amino acid insertion into the middle of a homodimeric archaeal histone fold motif.

Influence of ions, hydration, and the transcriptional inhibitor P4N on the conformations of the Sp1 binding site.

Three crystal structures containing the entire Sp1 consensus sequence d(GGGGCGGGG) with two or three additional base-pairs on either the 5' or 3' ends and overhangs have been determined. Despite the different lengths of DNA in the pseudo-dodecamers and pseudo-tridecamer, all three structures form A-DNA duplexes that share a common set of crystal contacts, including a T*(G.C) base triplet and a 5'-overhang that flips out and away from the helical axes to form a Hoogsteen base-pair with the 3'-overhang of a symmetry mate.

The histone octamer is invisible when NF-kappaB binds to the nucleosome.

The transcription factor NF-kappaB is involved in the transcriptional control of more than 150 genes, but the way it acts at the level of nucleosomal templates is not known. Here we report on a study examining the interaction of NF-kappaB p50 with its DNA recognition sequence in a positioned nucleosome. We demonstrate that NF-kappaB p50 was able to bind to the nucleosome with an apparent association constant close to that for free DNA.