The Use of Procion Blue as a Molecular Probe in the Study of Ribosomal Structure.

1. The triazinyl dye, procion brilliant blue MR, has a selective initial action on the proteins of rat liver ribosomes in situ, and can be used for detecting shielding effects in normal and modified particles. Alterations in the shielding pattern can be analyzed by disc-electrophoresis. 2. Irreversible dissociation of the ribosomes in Mg2+-deficient media makes a normally resistant protein ("protein 5") available to the reagent. This unmasking occurs even in the cold. 3. When the particles are incubated at 35° in the presence of aminoacridines, or in media with increased ionic strength, another previously shielded protein ("protein 10") is unmasked by a time and temperature dependent reaction. 4. The unmasking of protein 10 by incubation in media with increased ionic strength is partially reversible by a time and temperature dependent reaction. Although some detachment occurs in connection with the unmasking, the reversibility is probably confined t non-detached molecules. The activity of the particles of endogenous or poly U-dependent amino acid incorporation is not seriously impaired under these conditions. 5. The experiments indicate that organic reagents can be used to provide information about protein location and structural alterations in ribosomes, which confirm and extend structural data obtained by use of proteolytic enzymes. [ABSTRACT FROM AUTHOR]