II.24. Relation of nuclear proteins and lysine level in Hiproly barley.
Robert G. McDaniel and Marsha Chery, Department of Agronomy and Plant Genetics, University of Arizona, Tucson, Arizona 85721, USA.
A previous communication has detailed preliminary evidence for the association of basic nuclear proteins with enhanced lysine percentages in Hiproly barley (CI 3947), compared with a near -isogenic line, CI 4362 (BGN No. 1, pp. 30-31). The discovery and steps in development of lysine-rich barley have been summarized by Munck (BGN No. 2, pp. 54-59). Additionally, he has presented information on specific protein differences of Hiproly (Hereditas, 72:1-128, 1972). The present report presents our findings on lysine content of nuclear proteins as a basis for improved amino acid balance in cereals, specifically barley.
Figure 1 illustrates the distinctive characteristics of basic nuclear proteins (mainly histones), extracted from nuclei of germ-rich fractions of dry seeds of: l. Hiproly; 2. CI 4362; and 3. Manchuria, (CI2330).
Nuclear protein extractions were carried out as reported previously (BGN No. 1, pp. 30-31), with the substitution of 0.4M H2S04 for the HCl used in solubilization of histones. Amino acid analyses have established the basic nature of these proteins and have allowed us to separate them into lysine rich fractions, as noted in Figure 1. Co-electrophoresis of these barley nuclear proteins with known histone preparations has confirmed their identity as histones.
As can be seen in the Figure, the proportions of histone fractions of Hiproly differ markedly from CI 4362, Manchuria, and from other barley nuclear preparations not shown here, but which we have also tested. The amount of lysine-rich histones in nuclei of Hiproly expressed as a percentage of total histones is relatively greater (around 30%) than the proportion of lysine-rich histones from other barley lines.
When contribution of nuclear protein content to total cellular proteins in germ-rich barley fractions is calculated, the increased percentage of lysine-rich histones is sufficient to account for the increased percentage of lysine in seeds of Hiproly compared to other barley genotypes. Increased protein content of Hiproly would not be a factor here, as CI 4362 also exhibits similar levels of seed protein, while nuclear protein proportions remain relatively unaltered. Lysine-rich histones are considered by some researchers as the most effective repressors of gene transcription. If they indeed act thus, then the possible growth limiting effects of high proportions of lysine-rich histones would place a serious limitation on breeding efforts for high-lysine strains. Our studies on such possibilities are continuing. We believe, based on our studies of genetic control of barley histones, that analysis of these nuclear proteins has potential as a biochemical screening tool for establishing and maintaining optimum balance of limiting amino acids in barley and other cereals.
