title: Differentiation of rat myoblasts. Regulation of turnover of ribosomal proteins and their mRNAs.
abstract: The regulation of ribosomal proteins (r-proteins) and their mRNAs (rp-mRNAs) was studied in the L6 myoblast, a mammalian cell line which can undergo myogenesis. Upon terminal differentiation, the rate of accumulation of mature ribosomes dropped to approximately 25% of the rate found in undifferentiated myoblasts. Despite the drop in the rate of ribosome accumulation and the rate of rRNA synthesis following terminal differentiation, the rate of r-protein synthesis remained constant. The excess r-protein synthesized in myotubes was quickly degraded. The levels of rp-mRNAs were assessed before and after differentiation. Over 90% of the rp-mRNAs were found on polysomes in both myoblasts and myotubes and represented similar fractions of total poly(A)-rich mRNA. The half-lives of the rp-mRNAs averaged approximately 11 h in both myoblasts and myotubes. In vitro nuclear transcription measurements of a representative rp-mRNA (L32 mRNA) revealed that following differentiation, its rate of synthesis relative to the overall transcription rate dropped by approximately 26% in myotubes while the rate of transcription of rRNA dropped by approximately 77%. These results indicate that the coordination of r-protein and rRNA synthesis observed in myoblasts was uncoupled in myotubes at the level of transcription.
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D006207:Half-Life; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D012333:RNA, Messenger; D012269:Ribosomal Proteins