Loss of the mRNA-like region in mitochondrial tmRNAs of jakobids (original) (raw)

  1. YANNICK JACOB2,3,
  2. ELIAS SEIF2,
  3. PIERRE-OLIVIER PAQUET2, and
  4. B. FRANZ LANG1,2
  5. 1Program in Evolutionary Biology, Canadian Institute for Advanced Research
  6. 2Département de Biochimie, Université de Montréal, Montréal, Québec, Canada H3T 1J4

Abstract

It has been postulated that a highly reduced form of transfer messenger RNA (tmRNA), a bacterial molecule involved in the rescue of stalled ribosomes during translation, is expressed in the mitochondrion of the jakobid Reclinomonas americana. Here we show that genes encoding both one-piece and two-piece tmRNAs are present in six different jakobid mitochondrial DNAs. Mitochondrial tmRNAs have retained the highly conserved tRNAAla-like domain, but they apparently lack the mRNA-like region present in all bacterial tmRNAs. Comparative analysis of jakobid mitochondrial genomes shows that a potential mRNA-like region in R. americana (orf64) is located at distant genomic positions in other jakobids. Our results strongly suggest that orf64 is a tatA homolog. Through Northern hybridization we confirm the postulated reduced size of both a one-piece tmRNA in Jakoba libera and a two-piece tmRNA in Seculamonas ecuadoriensis. The J. libera tmRNA is post-transcriptionally modified by addition of a 3′ CCA tail, processed in vitro by RNase P RNA, and specifically charged with alanine in vitro by alanyl-tRNA synthetase. Our results strongly support the functionality of these reduced mitochondrial tmRNAs.

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