| Citation | Jean Thomas has made significant contributions to the elucidation of the role of all five histones in chromatin structure, and to the characterisation of chromatin folding in solution. She demonstrated specific subcomplexes of the inner histones in solution - in particular the arginine-rich tetramer, which was central to the formulation by R.D. Kornberg of a model for chromatin structure - and then showed that the protein core of the nucleosome was a histone octamer. This was isolated free of DNA, extensively characterised, and later regular aggregates were prepared that were suitable for image analysis (carried out by Klug and Finch). This led to a structure for the protein core of the nucleosome in which histone assignments drew heavily on Thomas's cross-linking studies. Turning her attention to the outer histone, H1, which is essential for higher order chromatin folding, she demonstrated its stoichiometry in chromatin (hitherto controversial); the presence of continuous runs of H1 in both extended and condensed chromatin; and the unexpected ability of H1 to exchange with other H1 molecules. Systematic studies of H1-dependent chromatin folding in solution (with Butler), using fragments of defined lengths, have provided valuable information about the nature of the folding and the stability of the folded state, and the probable location of linker DNA. |