Analysis of the mitochondrial and nuclear genomes of two basidiomycetes, Coprinus cinereus and Coprinus stercorarius

The mitochondrial and nuclear genomes of Coprinus stercorarius and C. cinereus were compared to assess their evolutionary relatedness and to characterize at the molecular level changes that have occurred since they diverged from a common ancestor. The mitochondrial genome of C. stercorarius (91.1 kb) is approximately twice as large as that of C. cinereus (43.3 kb). The pattern of restriction enzyme recognition sites shows both genomes to be circular, but reveals no clear homologies; furthermore, the order of structural genes is different in each species. The C. stercorarius mitochondrial genome contains a region homologous to a probe derived from the yeast mitochondrial var1 gene, whereas its nuclear genome does not. By contrast, the C. cinereus nuclear, but not mitochondrial, genome contains a region homologous to the var1 probe. Only a small fraction of either the nuclear or mitochondrial genomes, perhaps corresponding to the coding sequences, is capable of forming duplexes in interspecies solution reassociations, as measured by binding to hydroxylapatite. Those sequences capable of reassociating were found to have approximately 15% divergence for the mitochondrial genomes and 7%–15% divergence for the nuclear genomes, depending on the conditions of reassociation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46959/1/294_2004_Article_BF00447385.pd

Achlya mitochondrial DNA: gene localization and analysis of inverted repeats

Mitochondrial DNA from four strains of the oomycete Achlya has been compared and nine gene loci mapped, including that of the ribosomal protein gene, var1 . Examination of the restriction enzyme site maps showed the presence of four insertions relative to a map common to all four strains. All the insertions were found in close proximity to genic regions. The four strains also cotained the inverted repeat first observed in A. ambisexualis (Hudspeth et al. 1983), allowing an examination by analysis of retained restriction sites of the evolutionary stability of repeated DNA sequences relative to single copy sequences. Although the inverted repeat is significantly more stable than single copy sequences, more detailed analysis indicated that this stability is limited to the portion encoding the ribosomal RNA genes. Thus, the apparent evolutionary stability of the repeat does not appear to derive from the inverted repeat structure per se.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47563/1/438_2004_Article_BF00330510.pd

Yeast mitochondrial tRNATrp injected with E. coli activating enzyme into Xenopus oocytes suppresses UGA termination

It is now clear that the genetic code used in mitochondria differs in a number of ways from the standard code1-3, the most prominent being the use of the opal codon UGA to specify tryptophan4-7. This change in the mitochondrial genetic code is accommodated by the presence of an anticodon U*CA in mitochondrial (mt) tRNATrp from yeast8 and Neurospora crassa1. Furthermore, the translation of a mtDNA-encoded mRNA has been achieved in a eukaryotic cell-free system9: the mRNA of subunit II of yeast cytochrome c oxidase, which contains UGA codons in its reading frame, can be translated into a full-length protein if the system is supplemented with the Schizosaccharomyces pombe 10 cytoplasmic UGA suppressor tRNASer. It remains to be demonstrated whether a mitochondrial tRNA would be able to function in cytoplasmic protein synthesis. In the case of mt tRNATrp, this would cause the production of readthrough proteins due to the suppression of the UGA termination codon present in certain cytoplasmic mRNAs. Using the Xenopus oocyte microinjection system11-12, we show here that the mt tRNA Trp from Saccharomyces cerevisiae, when injected together with rabbit globin mRNA, suppresses UGA termination with high efficiency, thus leading to the production of a β-globin-related readthrough protein of molecular weight (Mr) 18,500. However, the suppressor activity of this tRNA within the oocyte cytoplasm is strictly dependent on the co-injection of an exogenous (Escherichia coli) acylating enzyme which is needed to charge the mt tRNATrp in vivo. The absence of an endogenous enzyme capable of acylating the yeast mt tRNATrp suggests that there is a biological barrier for the activity of a mt tRNA in the cytoplasm if a tRNA exchange between the two cellular compartments occurred. © 1981 Nature Publishing Group.SCOPUS: ar.jinfo:eu-repo/semantics/publishe