Research:
Core and Linker Histones and Chromatin Fiber Structure
The
intrinsic conformational dynamics of the chromatin fiber are mediated by the
core histone N-terminal tail domains (NTDs), and by linker histones. Our the
lab uses recombinant core and linker histones to assemble length- and
compositionally-defined chromatin model systems. We then analyze the model
systems using biochemical and biophysical approaches to obtain solution
structural information. We continue to use the 5S DNA-based system that we
have been cataloguing for 15 years, and have also started working with a 601
DNA-based system. Both DNAs position nucleosomes, leading to defined model
systems when histone octamers are assembled onto tandemly repeated DNA
templates.
To better understand core histone NTD function we are making specific NTD
mutants and asking whether they disrupt chromatin condensation in vitro.
Through use of recombinant histones and directed mutagenesis, over the
coming years we expect to systematically dissect the function and mechanism
of action of each core histone NTD during chromatin condensation.
Our studies of linker histone function also use recombinant proteins, and
currently are focused on the mechanism through which the linker histone
C-terminal domain (CTD) mediates chromatin fiber structure and dynamics. The
amino acid composition of the linker histone isoform CTDs is remarkably
similar and quite distinct (see below), even though the amino acid sequence
is not conserved. This has led us to focus on the role of intrinsic protein
disorder in CTD function. Our working model is that linker histone CTD
binding to linker DNA induces formation of secondary structure motifs
throughout the CTD that mediate subsequent stabilization of folded chromatin
fibers and interactions with other proteins.
Over the long term, elucidating
the molecular basis for how the core histone NTDs and linker histone CTD are
capable of binding to multiple macromolecular partners in different
functional contexts has become a major emphasis of the lab.
