A comparative study of ribonuclease hydrolysis of rat brain-cortex and liver membrane-bound ribosomes.

Because it has been proposed that the ribosome-membrane interaction is different in endoplasmic reticulum derived from a non-secretory and secretory cell we undertook a study to determine whether attachment of the ribosome to the membrane involved ribosomal RNA and if the rRNA in ribosomes derived from the two classes of cell possessed an altered susceptibility to RNAase (ribonuclease) hydrolysis. We found that brain ribosomes appeared to possess more regions accessible to nuclease attack, independent of whether a sequence-dependent RNAase (T(1)) or a sterically hindered RNAase bound to Enzite polymer was employed. These results were independent of whether the ribosomes were membrane-bound or detached from the endoplasmic reticulum membranes, but at high RNAase concentration these differences became negligible. No conclusions, however, could be drawn as to whether ribosomal RNA is involved in the attachment of the ribosome to the endoplasmic reticulum membrane, because of the presence of endogeneous membrane-associated RNAases. Analysis of the rRNA fragments by polyacrylamide-gel electrophoresis suggests that the sites available for attack by low concentrations of nuclease in bound-ribosomes derived from brain cortex are different from those of liver.