Evidence for a quantitative tissue-specific distribution of high mobility group chromosomal proteins

The quantitative tissue specificity of the high mobility group (HMG) chromosomal proteins was investigated. Perchloric acid (PCA) extracts of four different chicken tissues and erythrocytes contained three proteins which comigrated on NaDodSO4-polyacrylamide gels with the HMG's 1,2, and E from erythrocyte nuclei. These three HMG's from embryonic skeletal muscle and erythrocytes also comigrated on two-dimensional gels, employing an acid-urea system in the first dimension and an NaDodSO4 system in the second. Interpretation of the two-dimensional gels suggested that the two low molecular weight proteins of this triplet arose from the HMG 2 band of the acid-urea gels. These have been designated HMG 2A and HMG 2B. Three proteins of similar molecular weights were also found in the PCA extracts of calf thymus. They were arranged in a similar but not identical pattern on two-dimensional gels. Thus, these three HMG's appear to be neither tissue nor species specific. In addition, the 2.0% PCA extracts of all chicken tissues examined contain a 38 000-dalton (38K) nuclear protein which coisolates with the HMG's. These four proteins are found in different relative amounts in each of the four chicken tissues and erythrocytes. They are found in the same relative amounts, however, in embryonic skeletal muscles from different chicken strains with widely different highly repetitive sequence content, suggesting that none of these individual proteins is selectively localized to constitutive heterochromatin. The quantitative tissue specificity of the HMG's and the 38K protein, however, suggests that they may participate in regulating cell-specific gene expression.