The Giant RNA Transcript in a Balbiani Ring of Chironomus Tentans

Several years ago Beermann (1952), Breuer and Pavan (1953) and Mechelke (1953) described transient changes in the structure of giant chromosomes in insects. The modifications, designated puffs, were dependent on the cell type and developmental stage studied. These early investigations indicated that the puffs might be morphological manifestations of gene activity. Although it is likely that the puffs do represent differentially activated genes, the concept is primarily based on correlative data between chromosome structure and different cellular functions in cytoplasm. With the advent of molecular biology and the knowledge of the basic features of gene expression, it seems possible to test the puffing concept in a more straightforward way. The most likely hypothesis is that RNA is synthesized in the puffs, transported to cytoplasm and there specifies protein synthesis. Such studies have been initiated and will be discussed below.