The 19S ring-type particles of Drosophila. Cytological and biochemical analysis of their intracellular association and distribution.

The intracellular distribution and interaction of 19S ring-type particles from D. melanogaster have been analysed. Immunological and biochemical analyses show that the 19S particles are of a predominant cytoplasmic origin. Immunofluorescence experiments, using the particle-specific antibody Dm28K2, reveal a characteristic speckled cytoplasmic fluorescence pattern. Investigation of different biochemically isolated, cytoplasmic subfractions by sucrose gradient centrifugation and immunoblotting show that the 19S particles can exist as 'free' unbound structures as well as in association with Triton-X-100-extractable polyribosomal fractions. The tight association with the polyribosomes can only be broken by extraction of the polysomes in EDTA, which releases the particles as whole entities. The data suggest that the 19S ring-type particles of Drosophila may represent a new class of scRNPs involved in translational processes.