Biomedical subjects

B F Lang

Publications and source records attributed to B F Lang.

60 records · Page 4Linked to original sources

PubMed1984

The mitochondrial genome of the fission yeast Schizosaccharomyces pombe: highly homologous introns are inserted at the same position of the otherwise less conserved cox1 genes in Schizosaccharomyces pombe and Aspergillus nidulans.

The DNA sequence of the second intron in the mitochondrial gene for subunit 1 of cytochrome oxidase (cox1), and the 3' part of the structural gene have been determined in Schizosaccharomyces pombe. Comparing the presumptive amino acid sequence of the 3' regions of the cox1 genes in fungi reveals similarly large evolutionary distances between Aspergillus nidulans, Saccharomyces cerevisiae and S. pombe. The comparison of exon sequences also reveals a stretch of only low homology and of general size variation among the fungal and mammalian genes, close to the 3' ends of the cox1 genes. The second intron in the cox1 gene of S. pombe contains an open reading frame, which is contiguous with the upstream exon and displays all characteristics common to class I introns. Three findings suggest a recent horizontal gene transfer of this intron from an Aspergillus type fungus to S. pombe. (i) The intron is inserted at exactly the same position of the cox1 gene, where an intron is also found in A. nidulans. (ii) Both introns contain the highest amino acid homology between the intronic unassigned reading frames of all fungi identified so far (70% identity over a stretch of 253 amino acids). However, in the most homologous region, a GC-rich sequence is inserted in the A. nidulans intron, flanked by two direct repeats of 5 bp. The 37-bp insert plus 5 bp of direct repeat amounts to an extra 42 bp in the A. nidulans intron. (iii) TGA codons are the preferred tryptophan codons compared with TGG in all mitochondrial protein coding sequences of fungi and mammalia.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1984

The mitochondrial genome of the fission yeast Schizosaccharomyces pombe. 2. Localization of genes by interspecific hybridization in strain ade7-50h- and cloning of the genome in small fragments.

A series of 18 small overlapping restriction fragments has been cloned, covering the complete mitochondrial genome of Schizosaccharomyces pombe. By hybridizing mitochondrial gene probes from Saccharomyces cerevisiae and Neurospora crassa with restriction fragments of Schizosaccharomyces pombe mitochondrial DNA, the following homologous genes were localized on the mitochondrial genome of S. pombe: cob, cox1, cox2 and cox3, ATPase subunit 6 and 9 genes, the large rRNA gene and both types of open reading frames occurring in mitochondrial introns of various ascomycetes. The region of the genome, hybridizing with cob exon probes is separated by an intervening sequence of about 2500 bp, which is homologous with the first two introns of the cox1 gene in Saccharomyces cerevisiae (class II introns according to Michel et al. 1982). Similarly, in the cox1 homologous region, which covers about 4000 bp, two regions were detected hybridizing with class I intron probes, suggesting the existence of two cox1 introns in Schizosaccharomyces pombe. Hybridization with several specific exon probes with a determined order has revealed that cob, cox1, cox3 and the large rRNA gene are all transcribed from the same DNA strand. The low intensities of hybridization signals suggest a large evolutionary distance between Schizosaccharomyces pombe and Saccharomyces cerevisiae or Neurospora crassa mitochondrial genes. Considering the length of the mitochondrial DNA of Schizosaccharomyces pombe (about 19.4 kbp) and the expected length of the localized genes and intron sequences there is enough space left for encoding the expected set of tRNAs and the small rRNA gene. The existence of leader-, trailer-, ori- and spacer sequences or further unassigned reading frames is then restricted to a total length of about 3000 bp only.

Ascomycota↗

PubMed1984

The mitochondrial genome of the fission yeast Schizosaccharomyces pombe. 3. Gene mapping in strain EF1 (CBS 356) and analysis of hybrids between the strains EF1 and ade7-50h-.

The Schizosaccharomyces pombe strain EF1 (CBS 356) is haploid, prototrophic, respiratory competent, and of homothallic mating type. From restriction enzyme analysis the length of the mitochondrial genome is 17.3 kilobase pairs, which is in good agreement with the value of 17.1 kilobase pairs determined by electron microscopy. The mitochondrial genome of strain EF1 is thus about 2.3 kilobase pairs shorter than that of strain ade7-50h- (about 19.4 kilobase pairs). A restriction map was constructed for 11 enzymes: For most, but not all of them, the pattern is nearly identical to that of strain ade7-50h-. The genes for the large ribosomal RNA, the subunits 1, 2, and 3 of cytochrome c oxidase, subunits 6 and 9 of ATP synthetase, and cytochrome b were localized by hybridization with mitochondrial DNA probes from Saccharomyces cerevisiae. The gene order was found to be the same in both yeast strains. From Southern hybridization of strain ade7-50h- with nick-translated mitochondrial DNA from strain EF1 it is evident that strain EF1 does not possess the intron, which is present in the cytochrome b gene of Schizosaccharomyces pombe strain ade7-50h-. Crosses between strain ade7-50h- and EF1 demonstrate that both the nuclear and the mitochondrial genomes are able to recombine. The mitochondrial genomes of 2 out of 30 independently isolated hybrids between the two strains are described as the result of recombination between the two parental mitochondrial genomes.

Adenosine Triphosphatases↗

PubMed1983

Expression of the "split gene" cob in yeast mtDNA. Nuclear mutations specifically block the excision of different introns from its primary transcript.

Five nuclear mutants falling into five different complementation groups are shown to block the maturation of long form mitochondrial cob RNA at five different processing steps. At the same time they prevent complete processing of the oxi 3 RNA, thus exhibiting the same phenotype as mitochondrial box mutants (cyt b- and oxi 3-). The different nuclear factors in question have varying ranges of specificity for the removal of introns from cob RNA, from only one to at the most three introns. Two mutated nuclear elements are shown to be specific for the processing of introns present only in the long form cob gene. One such mutation shows, as expected, no deleterious effect on the processing of the short form cob RNA exchanged into the mutant via cytoduction. The role of nuclear coded factors in the possible translation or activity of introncoded products ("maturases") is discussed for two mutants. Striking parallels are found between diverse polypeptide products, presumably translated from accumulated cob RNA intermediates, in pet- and mit- mutants blocked in the excision of the same intron.

Base Sequence↗

PubMedDate not supplied

Mitochondrial class II introns encode proteins related to the reverse transcriptases of retroviruses.

Organelle introns share several distinctive features that set them apart from their counterparts in nuclear-encoded pre-messenger RNAs (reviewed in ref. 1): their termini do not obey the GU...AG rule; the introns are 'structured' (members of the same family or 'class' can theoretically adopt very similar RNA secondary conformations and several of the postulated pairings have been confirmed by studies of splicing mutants and their revertants (see, for example, ref. 4); many introns from both classes contain long open reading frames. We report here that the proteins potentially encoded by four class II introns are related to several RNA-dependent polymerases of viral and transposable element origins.

Base Sequence↗

PubMedDate not supplied

A comparative genomics approach to the evolution of eukaryotes and their mitochondria.

The Organelle Genome Megasequencing Program (OGMP) investigates mitochondrial genome diversity and evolution by systematically determining the complete mitochondrial DNA (mtDNA) sequences of a phylogenetically broad selection of protists. The mtDNAs of lower fungi and choanoflagellates are being analyzed by the Fungal Mitochondrial Genome Project (FMGP), a sister project to the OGMP. Some of the most interesting protists include the jakobid flagellates Reclinomonas americana, Malawimonas jakobiformis, and Jakoba libera, which share ultrastructural similarities with amitochondriate retortamonads, and harbor mitochondrial genes not seen before in mtDNAs of other organisms. In R. americana and J. libera, gene clusters are found that resemble, to an unprecedented degree, the contiguous ribosomal protein operons str, S10, spc, and alpha of eubacteria. In addition, their mtDNAs code for an RNase P RNA that displays all the elements of a bacterial minimum consensus structure. This structure has been instrumental in detecting the rnpB gene in additional protists. Gene repertoire and gene order comparisons as well as multiple-gene phylogenies support the view of a single endosymbiotic origin of mitochondria, whose closest extant relatives are Rickettsia-type alpha-Proteobacteria.

Animals↗