ABSTRACT
The three-dimensional structure of tRNA (Figure 1b) is even more complex because of additional interactions between the various units of secondary structure.
Transcription and processing of tRNA in prokaryotes The rRNA transcription units in E. coli contain some tRNA genes that are transcribed and processed at the time of rRNA transcription (Section G8). Other tRNA genes occur in clusters of up to seven tRNA sequences separated by spacer regions. Following transcription by the single prokaryotic RNA polymerase, the primary RNA transcript folds up into the characteristic stem-loop structures (Figure 2) and is then processed in an ordered series of cleavages by ribonucleases (RNases), which release and trim the tRNAs to their final lengths. The cleavage and trimming reactions at the 5¢ and 3¢ ends of the precursor tRNAs involves RNases D, E, F and P. RNases E, F and P are endonucleases, cutting the RNA internally, whilst RNase D is an exonuclease, trimming the ends of the tRNA molecules.
