Blotting Index of Dissimilarity: use to study immunological relatedness of plant and animal High Mobility Group (HMG) chromosomal proteins.

The High Mobility Group (HMG) proteins of vertebrate animals have been the subject of intensive study because of evidence that they may be structural proteins of transcriptionally active chromatin. Organisms other than vertebrate animals have chromatin proteins which meet the operational criteria of salt extractability and trichloroacetic acid solubility to be termed HMG proteins. However, because the properties of these proteins resemble those of vertebrate HMGs to varying degrees and because no definition of "HMG" based on biological function is available, a real question exists as to whether the proteins from other organisms should be considered HMGs. Because wheat HMG proteins have several biochemical properties in common with vertebrate HMGs and yet vary in other properties, we have used an immunological approach to study the relatedness of these two groups of proteins. We have raised polyclonal antibodies to the denatured wheat HMG proteins and have used an immunoblotting procedure to compare the affinities of these antibodies to the homologous wheat proteins and to the heterologous chicken HMG proteins. We have expressed the immunological relatedness of members of these two groups of proteins as the Blotting Index of Dissimilarity. This index is intended to be analogous to the Index of Dissimilarity determined by microcomplement fixation, and a direct comparison of the two procedures results in similar values. The magnitudes of the Blotting Indexes of Dissimilarity indicate that the antigenic features of the plant and animal HMG proteins have little in common.