A NEW-TYPE OF RIBONUCLEOPROTEIN CONSTITUENT OF THE POLYTENE NUCLEUS OF THE SALIVARY-GLANDS OF CHIRONOMUS-THUMMI AND CH-TENTANS

Using electron spectroscopic imaging, a new type of small granular str uctural constituent has been observed in the extrachromosomal zone of the polytene nucleus of the salivary gland cells of Chironomus thummi and Chironomus tentans. These granules appear isolated or in small clu mps and are often seen to be connected with surrounding thin fibrils. They are stained by the EDTA procedure, which is preferential for nucl ear ribonucleoprotein (RNP) constituents, and by the bismuth oxynitrat e method for visualizing phosphorylated compounds. The granules are 15 -23 nm in diameter and are digested by prolonged post-embedding RNAse hydrolysis. These structural elements contain the highest concentratio n of phosphorus in the interchromosomal space as revealed by electron energy loss spectroscopy. The small granules exhibit several morpholog ical and cytochemical features in common with interchromatin granules, but they are not labeled with antibodies directed against extranucleo lar small nuclear RNPs (snRNPs), as are interchromatin granules.