Mitochondrial RNAs of myxomycetes terminate with non-encoded 3′ poly(U) tails

We examined the 3′ ends of edited RNAs from the myxomycetes Stemonitis flavogenita and Physarum polycephalum using a modified anchor PCR approach. Surprisingly, we found that poly(A) tails are missing from the cytochrome c oxidase subunit 1 mRNA (coI) from both species and the cytochrome c oxidase subunit 3 mRNA (cox3) from P.polycephalum. Instead, non-encoded poly(U) tails of varying length were discovered at the 3′ ends of these transcripts. These are the first described examples of 3′ poly(U) tails on mature mRNAs in any system.