Chromosome activity and cell function in polytenic cells: V. Developmental changes in RNA synthesis and turnover

Abstract

RNA synthesis in the salivary glands ofChironomus tentans larvae was studied at two developmental stages which differ greatly in the sensitivity of protein synthesis to an inhibition of RNA synthesis. The size distribution of heterodisperse RNA synthesized at the two stages is similar. However, at the stage (s) not requiring newly synthesized RNA for protein synthesis a large portion of the heterodisperse, high molecular weight RNA is degraded within minutes after its synthesis. In contrast, at the stage (s) where newly synthesized RNA is required for protein synthesis, no such RNA is rapidly degraded. These conclusions are based upon (1) kinetics of uridine incorporation into RNA and the UTP poool, (2) gel electrophoresis of this RNA, and (3) chase experiments employing actinomycin D. It is proposed that in these polytenic cells protein synthesis during development is, in part, controlled posttranscriptionally by selective degradation of newly synthesized RNA. However, autoradiographic experiments with larvae of the stage where no rapid degradation of newly synthesized RNA was observed, suggest that the posttranscriptional control mechanism is superimposed upon a, possibly constant, pattern of differential RNA synthesis.