In Vitro mRNA Editing Using S100 Extracts

Alteration of genomically encoded nucleotide sequence in mRNA is called RNA editing. RNA editing was first described in mitochondrial mRNAs of kinetoplastid protozoa (Trypanosoma, Leishmania, Crithidia ) where numerous additions or deletions of uridine residues created translatable mRNA (1 , 2 ). Conversions of cytidines to uridines in mitochondrial mRNAs of plants alter genomically encoded amino acid sequence and explain the ambiguity observed in the use of the universal genetic code in the genome of plant mitochondria (3 , 4 ). In addition, similar C to U editing has been observed in chloroplasts (5 ). Recently, insertions of cytidines have been found in mitochondrial mRNAs of the acellular slime mold Physarum polycephalum (6 ). Insertions of two nontemplated guanosines in the mRNA of the “P” gene of paramyxovirus SV5 join two independent open reading frames for the P protein, the larger gene product of the “P” gene besides the smaller variant, the V protein, which is encoded solely by the first open reading frame (7 ). Similarly, in a subset of P gene transcripts of measles virus, the insertion of a nontemplated G residue connects the reading frame for the P protein to a cysteine-rich segment (8 ). Another example of sequence alteration of mRNA is the conversions of adenosines to inosines in regions of double-stranded mRNA of the basic fibroblast growth factor in Xenopus oocytes (9 ).