A NOVEL WAY TO GENERATE NONSPECIFICALLY RADIOLABELED PROTEINS FOR USEAS MOLECULAR-WEIGHT MARKERS

A method for labeling proteins using radioactive nucleotides in the pr esence of divalent cations such as Cu2+, Zn2+ and Cd2+ is described. S mall amounts of marker proteins can be rapidly labeled using the metho d and they can be used for molecular-weight determination of radioacti ve proteins of unknown molecular weights, as for example, any protein labeled with S-35-methionine in vivo or any protein radiolabeled by P- 32 in protein phosphorylation experiments. The gels in which the label ed markers and the proteins of unknown molecular weight are electropho resed could be directly exposed to X-ray films and comparisons made fr om a single autoradiogram, avoiding a two step procedure of Coomassie blue staining followed by autoradiography and aligning of the two sets of bands. This metal-ion-mediated labeling of proteins described in t he present communication is not by any site-specific interaction of th e nucleotide with the proteins and the protein is denatured after the complex formation. The adducts, once formed, are stable under conditio ns of SDS-PAGE or EDTA treatment. It is suggested that proteins labele d under conditions described in this communication are ternary complex es involving aromatic residues of the proteins, nucleotides and the di valent cations.