<P> There may be one or more copies of the operon dispersed in the genome (for example, Escherichia coli has seven). </P> <P> Archaea contains either a single rDNA operon or multiple copies of the operon . </P> <P> The 3' end of the 16S ribosomal RNA (in a ribosome) binds to a sequence on the 5' end of mRNA called the Shine - Dalgarno sequence . </P> <P> In contrast, eukaryotes generally have many copies of the rRNA genes organized in tandem repeats; in humans approximately 300--400 repeats are present in five clusters (on chromosomes 13, 14, 15, 21 and 22). Because of their special structure and transcription behaviour, rRNA gene clusters are commonly called "ribosomal DNA" (note that the term seems to imply that ribosomes contain DNA, which is not the case). </P>

Rrna is a structural molecule that is not translated into an amino acid sequence