Ribonuclear protein formation at locus 2-48 BC in Drosophila hydei

Abstract

IN Drosophila hydei salivary glands, a puff can be induced by treatment with vitamin B₆ (ref. 1) at locus 2-48 BC. This puff is one of the series that can also be induced by temperature shock, anaerobiosis or treatments interfering with the respiratory metabolism². A product of this puff seems to be a giant ribonucleoprotein (RNP) complex (diameter up to 4,000 Å) with a very specific morphology³. This complex consists of a core and a cortex, formed by a wreath of small particles (diameter approximately 300 Å; ref. 4). Cytochemical analysis has shown that the core of the complex is essentially free of RNA whereas the cortex does contain RNA⁴. Using phospho-tungstic acid (PTA) as a specific stain for proteins, it could also be shown that the proteins from the cortex are relatively rich in arginine and lysine residues whereas those in the core are relatively poor in such residues⁵. No similar puff product has so far been found in any other locus of D. hydei. In addition to the giant RNP complexes small RNP particles (diameter up to 300 Å; not to be confused with the particles from the cortex) can also be seen in this puff^2,5. A comparison of data from both ultrastructural and autoradiographical studies on RNA formation at locus 2-48 BC has led to the conclusion that the small RNP particles present in this puff aggregate to the giant RNP complexes and thus give rise to the final puff product⁶. This conclusion is in agreement with the finding of a single RNA species in puffs obtained by microdissection of salivary glands⁷. Although the small RNP particles in the puff have not been studied extensively, it has been assumed that, based on the presence of RNA and arginine and lysine residues, the small particles form the cortex of the complex⁵, leaving the origin of the cortex proteins still obscure. Here I present the results of a comparison between the staining of the small RNP particles with that of the components of the giant complexes. These studies indicate that the same components of the small RNP particle become part of the core of the complex after aggregation.