A new type of RNA editing. 5S ribosomal DNA transcripts are edited to mature 5S rRNA.

The primary structure of the 5S rRNA from Arabidopsis thaliana was determined. A comparison of this nucleotide sequence with that of 5S rRNA gene showed two differences. Furthermore, we compared all plant 5S rRNA and 5S rDNA sequences known to date and found that lack of colinearity is widespread among higher plant 5S rRNAs and occurred mainly in the double stranded regions. To explain this, we suggest a mechanism which converts putative products of pseudogene ("cryptogene") to mature 5S rRNA molecule. This kind of editing mechanism functions primarily in stems of 5S rRNA in order, to correct mispairing and thereby restoring the Watson-Crick base pairs. This idea could explain why so many different 5S rRNA genes or gene like sequences and only one 5S rRNA species exist in the plant cell. The editing can serve as a new mechanism of regulation of 5S rRNA synthesis in addition to transcription of 5S rRNA gene.