RNA-TRANSCRIPTION IN PORCINE SKELETAL-MUSCLE NUCLEI DURING POSTNATAL-DEVELOPMENT

Postnatal developmental pretranslational regulation of skeletal muscle alpha-actin gene expression was investigated. Northern blot analysis of skeletal muscle alpha-actin and beta-tubulin mRNA from 1- and 28-da y-old pigs indicated that there are developmental increases in alpha-a ctin mRNA abundance (P < 0.03) and no significant changes in beta-tubu lin mRNA (P > 0.1). A system for isolation of nuclei from porcine skel etal muscle and for transcriptional ''run-on'' analysis was establishe d in order to investigate the regulatory mechanism of developmental ch anges in porcine skeletal muscle protein. Skeletal muscle nuclei were isolated from longissimus dorsi (LD) muscle of 1- and 28-day old pigs by adapting a method to isolate nuclei from cardiac muscle. Results fr om a [H-3]-UTP incorporation assay indicate that these nuclei preparat ions have the capacity to synthesize RNA and attain maximum incorporat ion after 40-45 min at 26 degrees C. Messenger RNA syntheses from skel etal muscle nuclei from 1- and 28-day-old pigs were not significantly different (P > 0.25). All nascent tRNA, rRNA, and mRNA in the nuclei w ere elongated since [H-3]-UTP incorporation was reduced after addition of 0.05 mu g/ml alpha-amanitin to the transcription mixture. Transcri ption ''run-on'' assay results indicated that more (P < 0.02) skeletal muscle alpha-actin pre-mRNA was synthesized in the 28-day-old pig ske letal muscle nuclei than in the 1 day-old pig skeletal muscle nuclei. These results indicate that the relative increase in skeletal muscle a lpha-actin mRNA observed in the older animals was due, at least in par t, to an increase in the transcriptional activity of the skeletal musc le alpha-actin gene.