Localization of ribonucleoprotein in the trilaminar kinetochore of PtK1

Abstract

A high-voltage electron microscope was used to study the distribution of ribonucleoprotein (RNP) in trilaminar kinetochores of metaphase and anaphase PtK1 cells. The results indicate that the inner plate of the trilaminar kinetochore contains a component which can be selectively stained by a method which preferentially stains RNP. This staining reaction is abolished by RNase digestion and cold perchloric acid (PCA) extraction. It is not eliminated by PCA treatment alone or by substituting other positively charged proteins (i.e., cytochrome c or lysozyme) for RNase. These results support the contention that RNase removes this component from the kinetochore and strongly suggest that the inner plate of the trilaminar kinetochore in PtK1 contains RNP. Treatment of PtK1 with colchicine induces structural changes within the kinetochore: Its trilaminar composition is supplanted by a single RNP-containing plate which is exaggerated in size. The significance of these observations with regard to the structure of the trilaminar kinetochore is discussed. When considered in light of other reports describing RNP in the centriole and pericentriolar material, the presence of RNP in the kinetochore suggests that this nucleoprotein may be a universal component of microtubule organizing centers. © 1979 Academic Press, Inc.