Abstract
The reading frame in the mRNA for the cytochrome b apoprotein in mitochondria of Physarum polycephalum is created by the insertion of 43 nucleotides in the mRNA relative to the mtDNA sequence encoding it (RNA editing). Most of these insertions (31) are single cytidines; however, single uridines are inserted at six sites, and the dinucleotides, CU and GC, are inserted at two sites and one site, respectively. These insertions create a 392-codon reading frame in the mature mRNA. The amino acid sequence inferred from this reading frame has similarity to cytochrome b apoproteins encoded by other mtDNAs. The insertions are quite evenly distributed throughout the length of the reading frame with an average spacing of 27 nucleotides. This mRNA has the highest percentage (23%) of noncytidine insertions of any Physarum RNA characterized to date. cDNAs corresponding to partially edited RNAs can be enriched by selective amplification. Some cDNAs that lack the GC dinucleotide insertion are fully edited at sites flanking the GC dinucleotide insertion site. Similarly some cDNAs lack the CT dinucleotide insertion or have a CC or TT insertion flanked by a fully edited sequence. These results imply that dinucleotide editing occurs by a process separate from the global insertion of cytidines.
Highlights
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) AF079798 and AF079799
If dinucleotide insertions were produced by the occasional placement of two single insertion sites at adjacent positions, the composition of the dinucleotide sites would reflect the composition of the single nucleotide insertion sites
This is clearly not the case because adenosine and guanosine nucleotides have only been observed to be inserted at dinucleotide insertion sites and because CC insertions, the type of dinucleotide insertion predicted to be most common based on single insertion nucleotide frequency, are not normally observed in Physarum RNA
Summary
(Received for publication, September 2, 1998, and in revised form, November 3, 1998). The reading frame in the mRNA for the cytochrome b apoprotein in mitochondria of Physarum polycephalum is created by the insertion of 43 nucleotides in the mRNA relative to the mtDNA sequence encoding it (RNA editing) Most of these insertions [31] are single cytidines; single uridines are inserted at six sites, and the dinucleotides, CU and GC, are inserted at two sites and one site, respectively. A unique type of RNA editing is found in mitochondria of the acellular slime mold Physarum polycephalum In this organism most of the RNA editing sites are single cytidine (C) insertions, but occasional single uridine (U) insertions and dinucleotide (AA, AU, CU, and GU) insertions are observed [2,3,4,5,6,7,8,9], as well as C to U substitutional editing [6].
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