CHARACTERIZATION OF A NOVEL SMALL RNA ENCODED BY DICTYOSTELIUM-DISCOIDEUM MITOCHONDRIAL-DNA

In this study, we analyzed a mitochondrial small (ms) RNA in Dictyoste lium discoideum, which is 129 nucleotides long and has a GC content of only 22.5%. In the mitochondrial DNA, a single-copy gene (msr) for th e ms RNA was located downstream of the gene for large-subunit rRNA. Th e location of nt,pr was similar to that of the 5S rRNA gene in prokary otes and chloroplasts, but clearly different from that in mitochondria of plants, liverwort and the chlorophycean alga Prototheca wikerhamii , in which small-subunit rRNA and 5S rRNA genes are closely linked. Th e primary sequence of ms RNA showed low homology with mitochondrial 5S rRNA from plants, liverwort and the chlorophycean alga, but the propo sed secondary structure of ms RNA was similar to that of cytoplasmic 5 S rRNA. In addition, ms RNA showed a highly conserved GAAC sequence in the same loop as in common 5S rRNA. However, ms RNA was detected main ly in the mitochondrial 25 000 x g supernatant fraction which was devo id of ribosomes. It is possible that ms RNA is an evolutionary derivat ive of mitochondrial 5S rRNA.