MRNA polymerase editing

Figure 20.20 Summary of transcription, RNA processing and polypeptide synthesis. Polymerisation of the DNA template by RNA polymerase produces pre-mRNA (the primary transcript) this is transcription. The pre-mRNA is now processed, which involves capping, polyadenylation, editing and splicing (see text). The resultant mRNA transfers from the nucleus to the cytosol, where amino acids are polymerised to produce a polypeptide using the instructions present in the codons of the mRNA.

Yet another type of editing has been observed in viral RNA from paramyxovirus. The virally encoded RNA polymerase sometimes "stutters" reading the same template base two or more times, with a resulting insertion of a base. Editing of transcripts usually serves an essential biological function, creating the correct sequence for translation of the mRNA and often generating multiple isoforms of proteins. 

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