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

Curr Genet. 1997 Jan;31(1):80-8. doi: 10.1007/s002940050179.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Chromosome Mapping
  • Cloning, Molecular
  • DNA, Mitochondrial / genetics
  • DNA-Binding Proteins / genetics*
  • Dictyostelium / genetics*
  • Electron Transport Complex IV / genetics*
  • Endonucleases / genetics
  • Endoribonucleases / genetics
  • Introns*
  • Membrane Proteins / genetics*
  • Molecular Sequence Data
  • Molecular Structure
  • Nucleotidyltransferases / genetics
  • Open Reading Frames*
  • Phylogeny
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Sequence Homology, Nucleic Acid
  • Viral Proteins / genetics*


  • Cox protein, Enterobacteria phage P2
  • DNA, Mitochondrial
  • DNA-Binding Proteins
  • Membrane Proteins
  • Saccharomyces cerevisiae Proteins
  • Viral Proteins
  • COX3 protein, S cerevisiae
  • Electron Transport Complex IV
  • Nucleotidyltransferases
  • mRNA maturase
  • Endonucleases
  • Endoribonucleases

Associated data

  • GENBANK/D16579
  • GENBANK/D50297