Electron spectroscopic imaging analyses of the distribution of phosphorus in Balbiani ring granules and in the surrounding nucleoplasm.

The in situ distribution of phosphorus was studied in unstained ultrathin sections of salivary glands of Chironomus tentans and Ch. thummi larvae using elemental mapping by means of an energy-filtering transmission electron microscope. This distribution was related to the structures observed using contrast enhancement with inelastically scattered electrons at 250 eV. This procedure demonstrated that a phosphorus-containing fibril about 2 nm thick is the common substructure of the following nuclear ribonucleoprotein structural constituents: the Balbiani ring granules, their precursor fibrils seen at the sites of transcription, especially at the Balbiani rings, and the fibres traversing the pore of the nuclear envelope. These phosphorus-containing thin fibrils are sensitive to RNase. Thicker substructural features of the Balbiani ring granules, occurring as a curved ribbon on a dense particle, appear to be formed by the dense packing of the fine fibrils. The Balbiani ring granules located near the nuclear envelope are often linked to it by fine filaments.