Maturation of Preribosomes

Abstract

Preribosomes may be defined as discrete, free ribonucleoprotein particles containing pre-rRNA. The assembly of preribosomes starts during transcription of rRNA genes and the growing pre-rRNA chain is already coated with ribosomal and non-ribosomal proteins. The selective interaction of individual r-proteins with the respective segments in pre-rRNA clearly shows (Chooi and Leiby 1981) that its protein coating involves specific protein-RNA and protein-protein interactions. Thus, assembly of preribosomes takes place simultaneously with transcription to release upon termination an already defined particle which may be designated as the primary preribosome (containing primary pre-rRNA).