ANALYSIS OF A TRANSFER-RNA GENE-LIKE SEQUENCE (T-ELEMENT) WITH TTA ATTHE ANTICODON POSITION IN THE MITOCHONDRIAL-DNA OF DICTYOSTELIUM-DISCOIDEUM

During the course of mitochondrial DNA sequencing of Dictyostelium dis coideum, a sequence with a tRNA-like structure and two genes for tRNA( Gln)(UUG) and tRNA(Trp)(CCA) were found downstream of the gene for lar ge subunit rRNA. The existence of tRNA(Trp) with CCA anticodon support s the finding that UGA codon is not a tryptophan codon in D. discoideu m mitochondria. Interestingly, the tRNA gene-like sequence (t-element) has TTA at the anticodon position. Northern blot analysis showed that , in low molecular mass mitochondrial RNA fraction of growth-phase cel ls and developmental stage cells, a mature transcript of the ele ment could not be detected in the tRNA region on an ureadenatured 15% polya crylamide gel, although there were several bands in the higher molecul ar mass region, indicating the actual transcription of the t-element. Southern blot analysis for total and mitochondrial DNA showed that the element exists as a single copy, only in the mitochondrial DNA but no t in the nuclear DNA.