In vitro synthesis and processing of ribosomal RNA in the housefly ovary

Abstract

Musca domestica ovaries labeled in vitro with 3H-uridine transcribe and process ribosomal RNA. The molecular weights of rRNA precursors, intermediates and products observed are: 38S (2.85 × 10 6), 32S (1.85 × 10 6) 30S (1.66 × 10 6), 28S (1.42 × 10 6), 20S (0.76 × 10 6) and 18S (0.70 × 10 6). Incubation of prelabeled ovaries with actinomycin D inhibits transcription and allows complete processing of 38S precursor through intermediates into 28S and 18S RNA in 40 min. The 38S RNA is cleaved into a 32S and 20S RNA. The 32S intermediate is further processed to a 30S precursor of mature 28S rRNA and the 20S RNA serves as a precursor to 18S RNA. The half-life of the 38S precursor has been calculated as 12 min. Approximately 26% of precursor molecular weight is lost during processing to mature rRNA. The results obtained demonstrate the production of insect 28S RNA through a 32S RNA intermediate using an in vitro system which allows complete processing of rRNA.