The Size and Chromosomal Location of the 75S RNA Transcription Unit in Balbiani Ring 2

Abstract

During the past several years we have been interested primarily in the functional significance of Balbiani ring 2, a giant puff specific to the salivary glands of Chironomus tentans. It has been demonstrated that a 75S RNA transcript is produced within Balbiani ring 2 (BR2) and that this RNA molecule is transported via nuclear sap into cytoplasm (for review, see Daneholt 1975). Recently it has also been shown that 75S RNA molecules (Daneholt et al. 1977) and BR2 RNA sequences (Wieslander and Daneholt 1977) reside in large-size polysomes. Since, in cytoplasm, BR2 sequences are confined to the 75S RNA fraction (Lambert and Edstrom 1974), it was inferred that 75S RNA from BR2 is incorporated into polysomal structures (Daneholt et al. 1977). Furthermore, since 75S RNA constitutes by far the most abundant nonribosomal, high-molecular-weight RNA species in cytoplasm (Daneholt and Hosick 1973) and most of it is present in polysomes (Daneholt...