ABSTRACT
Synthesis of equimolar quantities of three of the Ribonucleic acid (RNA) molecules found in ribosomes is generally achieved via the production of a single ribosomal RNA (rRNA) precursor molecule. In wild type Escherichia coli, processing of pre-rRNA occurs during the course of transcription, as is evident from the electron micrographs of J. H. Miller et al. The organization of rRNA genes in Bacillus subtilis is somewhat different from Escherichia coli. Most of the rRNA genes are clustered near the origin of replication and only a few pre-rRNA transcripts contain Transfer RNA molecules in the 16S-23S spacer region. Generally, both primary and secondary structures may play important roles in RNA processing. The complete nucleotide sequence for the transcribed portion of the rRNA gene repeat unit of Saccharomyces carlsbergene sis is known. Chloroplast ribosomal RNA transcription units have been completely sequenced in two higher plants, maize and tobacco, and their arrangement analyzed in a variety of other species.
