We propose to isolate and characterize the genes for the high mobility group (HMG) chromosomal proteins from two higher plants--wheat (Triticum aestivum) and Arabidopsis (Arabidopsis thaliana). In order to isolate cDNA for these proteins, we plan two alternative approaches. The first approach involves cloning cDNA in an expression vector (Lambda gt11) and probing using antibodies to the wheat HMG proteins. The second approach involves cloning cDNA in another bacteriophage vector (Lambda gt10) and probing with synthetic oligonucleotides made to correspond to partial amino acid sequences of the wheat HMG proteins. We believe that a knowledge of the structures of the genes of these abundant chromosomal proteins is important not only in itself but also because of the clues it may give us concerning the biological functions of HMG proteins. The exact nature of the functions of these proteins is as yet unknown, but there is evidence that they bind specifically to nucleosomes and may serve as structural proteins of transcriptionally active chromatin. We have shown that plant and animal HMG proteins differ considerably as judged by their amino acid contents, peptide maps and immunological characteristics. Nevertheless, their nucleosome binding properties have been evolutionarily conserved as evidenced by cross-species HMG-nucleosome binding in wheat and chicken. Determination of the amino acid sequences of the wheat HMG proteins from the nucleotide sequences of their genes will allow us to identify any homologies with animal HMG proteins. Because the overall structures of plant and animal HMG proteins are very different, any regions of homology are likely to be involved in their evolutionarily conserved biological functions. Thus, identifying regions of homology in plant and animal HMG proteins will be a step toward understanding the mechanism of HMG-nucleosome binding and the regulation of gene expression in eukaryotic organisms.
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| Spiker, S; Hopkins, R; Fischer, R et al. (1987) Synthesis of nucleosomal histone variants during wheat grain development. Biochim Biophys Acta 910:157-62 |
