Group-I introns in the cytochrome c oxidase genes of Dictyostelium discoideum: two related ORFs in one loop of a group-I intron, a cox1/2 hybrid gene and an unusually large cox3 gene.
The DNA sequences of cytochrome oxidase (subunits 1, 2 and 3) genes of the cellular slime mold Dictyostelium discoideum mitochondria were determined. The genes for subunits 1 and 2 have a single continuous ORF (COX1/2) which contains four group-I introns. The insertion sites of the two group-I introns (DdOX1/2.2 and DdOX1/2.3) coincide with those of fungal and algal group-I introns, as well as a liverwort group-I intron, in the cytochrome oxidase subunit 1. Interestingly, intron DdOX1/2.2 has two free-standing ORFs in a loop (L8) which have similar amino-acid sequences and are homologous to ai4 DNA endonuclease (I-Sce II) and bi4 RNA maturase found in group-I introns of Saccharomyces cerevisiae mitochondrial DNA. Two group-I introns (DdOX1/2.3 and DdOX1/2.4) also have a free-standing ORF in loop 1 and loop 2, respectively. These results show that these group-I introns and the intronic ORFs have evolved from the same ancestral origin, but that these ORFs have been propagated independently.
Ogawa
S
S
Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan.
Matsuo
K
K
Angata
K
K
Yanagisawa
K
K
Tanaka
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004272:DNA, Mitochondrial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D004023:Dictyostelium / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000235:genetics*; D004720:Endonucleases / Q000235:genetics; D004722:Endoribonucleases / Q000235:genetics; D007438:Introns; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009713:Nucleotidyltransferases / Q000235:genetics; D016366:Open Reading Frames; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014764:Viral Proteins / Q000235:genetics*
C070354:Cox protein, Enterobacteria phage P2; D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D014764:Viral Proteins; C093750:COX3 protein, S cerevisiae; D003576:Electron Transport Complex IV; D009713:Nucleotidyltransferases; C034038:mRNA maturase; D004720:Endonucleases; D004722:Endoribonucleases