Light-stimulated transcription of genes for two chloroplast polypeptides in isolated pea leaf nuclei.

Nuclei isolated from both light-grown and dark-grown leaves of Pisum sativum by Percoll density gradient centrifugation incorporate labelled UTP into RNA when supplemented with the other three nucleoside triphosphates. The RNA is heterodisperse, with transcripts up to at least 25S in size. Among these transcripts are sequences hybridizing to cloned DNA probes for wheat rRNA and two abundant chloroplast polypeptides of Pisum, viz. the small subunit of ribulose bisphosphate carboxylase and a polypeptide of the light-harvesting chlorophyll a/b binding complex. Transcription of small subunit and light-harvesting complex sequences is greater (18-fold and 9-fold, respectively) in nuclei from light-grown leaves than in nuclei from dark-grown leaves. Transcription of ribosomal genes, by contrast, is only doubled by growth in the light. Small subunit and light-harvesting complex sequences transcribed in dark-grown nuclei are not degraded in a 120 min chase. These results suggest that the stimulation of accumulation of small subunit and light-harvesting complex mRNAs by exposure of Pisum seedlings to light is mediated by an increase in transcription rather than by a decrease in RNA degradation.