ABSTRACT
Each ribosome consists of two subunits, a small subunit and a large subunit, each of which is a multicomponent complex of ribosomal ribonucleic acid (rRNA) and ribosomal proteins. A wide range of studies have built up a detailed picture of the fine structure of ribosomes, mapping the location of the various RNA and protein components and their interactions. In eukaryotes, the genes for 28S, 18S and 5.8S rRNA are typically clustered together and tandemly repeated in that one copy each of 18S, 5.8S and then 28S genes occur, followed by untranscribed spacer deoxyribonucleic acid, then another set of rRNA 18S, 5.8S, and 28S genes occur. In E. coli there are seven rRNA transcription units scattered throughout the genome, each of which contains one copy of each of the 23S, 16S and 5S rRNA genes and one to four copies of various transferRNA genes.
