Evolution of four types of RNA editing in myxomycetes

The myxomycete Physarum polycephalum requires extensive RNA editing to crea te functional mitochondrial transcripts, The cytochrome c oxidase subunit 1 (col) transcript exhibits a combination of editing forms not found togethe r in any other eukaryotic RNA: 66 insertions of ribonucleotides (59 Cs, a s ingle U, and three mixed dinucleotides) as well as base conversion of four Cs to Us (Gott et al,, J Biol Chem, 1993, 268:25483-25486). Through a phylo genetic survey of col DNA genes and RNA transcripts in representative myxom ycetes, we have decoupled the four types of editing in this lineage, Some m yxomycetes share insertional editing with P. polycephalum, yet lack C --> U conversion, consistent with previous reports of separation of insertional and base conversion editing in P. polycephalum extracts (Visomirski-Robic & Gott, RNA, 1995, 3:821-837), Most remarkably, we detect unique evolutionar y histories of the three different types of insertional editing, though the se have been indistinguishable in vitro. For example, Clastoderma debaryanu m exhibits insertions of Us, but not Cs or dinucleotides.