LOW MOLECULAR WEIGHT RNA IN CELL COMPONENTS OF CHIRONOMUS TENTANS SALIVARY GLANDS

The labelled low molecular weight RNA of isolated nuclear components (nucleoli, chromosomes, nuclear sap) and cytoplasm of Chironomus tentans salivary gland cells has been characterized by electrophoresis in high percentage polyacrylamide gel. 4 s RNA as well as 5 s RNA was recovered from the three nuclear components. The results suggest that 4 s RNA is formed from RNA of slower migration rate in chromosomes, nuclear sap and cytoplasm. In the nucleolus, on the other hand, label appears immediately in the 4 s position and the profile does not show any evidence of shifts with aging in the migration properties of the fractions. The life-time for 4 s RNA was found to be relatively short in the nucleolus as compared to other nucleolar RNA fractions as well as to 4 s RNA in other cellular locations. Incorporation studies with l-[methyl-3H]methionine as methyl donor for the polynucleotides showed that the larger part of the label of the low molecular weight chromosomal, nucleolar and cytoplasmic RNA was in a 4 s position, the material in the 5 s and intermediate regions remaining unlabelled. In all the nuclear components there is a fraction of 5 s RNA which does not shift position with aging and which does not undergo methylation, possibly identical to the ribosomal 5 s component. Both chromosomes and nucleoli contain fractions in the range between 5 and 16 s, but these are lacking in the cytoplasm. © 1969.