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An electron microscopic observation of the nucleolar material attached to the chromosomes of HeLa cells in metaphase.

A cluster of granules has been known by electron microscopy to occur in contact with the surface of metaphase chromosomes, and is considered to be an altered form of nucleolus in the mitotic phase. In the present examination three types of specimens of HeLa cells, namely, sections stained doubly with uranyl acetate and lead citrate, those stained with EDTA according to the regressive staining method of BERNHARD (1969), and those digested by RNase were compared by electron microscopy in regards to the relationship between the chromosomes and the granules. After the EDTA treatment chromosomes containing DNP were bleached, wheareas the granules maintained their electron density. Futhermore, the latter were digested by RNase, suggesting RNP content. The granules are 150A in diameter and resembled the ribosomes. They appear in prophase and are most distinct and abundant in metaphase.