Organ discrimination through organ-specific nonhistone chromosomal proteins

Prefractionation of chromosomal proteins in 5 m urea with stepwise increase in NaCl molarity has been used to facilitate the examination of nonhistone chromosomal proteins isolated from various rabbit tissues. Electrophoretic analysis on polyacrylamide gels under denaturing conditions of the protein fractions derived from brain, liver, heart, and submandibular salivary gland chromatins displays reproducible compositional differences in nonhistone chromosomal proteins. The enzymatic removal of 48% of protein-bound phosphate with alkaline phosphatase does not significantly alter the electrophoretic mobility of these proteins. With the present technique, it is estimated that chromatin polypeptides (of average M_r 100,000) occurring in greater than 3 × 10⁴ copies per genome can be detected. At this level of sensitivity, a significant fraction of total nonhistone chromosomal proteins manifests organ specificity.