Analysis of a tRNA gene-like sequence (t-element) with TTA at the anticodon position in the mitochondrial DNA ofDictyostelium discoideum

Abstract

During the course of mitochondrial DNA sequencing ofDictyostelium discoideum, a sequence with a tRNA-like structure and two genes for tRNAGin(UUG) and tRNATrp(CCA) were found downstream of the gene for large subunit rRNA. The existence of tRNATrp with CCA anticodon supports the finding that UGA codon is not a tryptophan codon inD. discoideum 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 cells and developmental stage cells, a mature transcript of the ele ment could not be detected in the tRNA region on an ureadenatured 15% polyacrylamide gel, although there were several bands in the higher molecular 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 not in the nuclear DNA.