Biomedical subjects

V Knoop

Publications and source records attributed to V Knoop.

27 records · Page 2Linked to original sources

PubMed1994

Promiscuous mitochondrial group II intron sequences in plant nuclear genomes.

Gene translocations from the organelles to the nucleus are postulated by the endosymbiont hypothesis. We here report evidence for sequence insertions in the nuclear genomes of plants that are derived from noncoding regions of the mitochondrial genome. Fragments of mitochondrial group II introns are identified in the nuclear genomes of tobacco and a bean species. The duplicated intron sequences of 75-140 bp are derived from cis- and trans-splicing introns of genes encoding subunits 1 and 5 of the NADH dehydrogenase. The mitochondrial sequences are inserted in the vicinities of a lectin gene, different glucanase genes and a gene encoding a subunit of photosystem II. Sequence similarities between the nuclear and mitochondrial copies are in the range of 80 to 97%, suggesting recent transfer events that occurred in the basic glucanase genes before and in the lectin gene after the gene duplications in the evolution of the nuclear gene families. Overlapping regions of the same introns are in two instances also involved in intramitochondrial sequence duplications.

Base Sequence↗

PubMed1994

RNA editing of a conserved reading frame in plant mitochondria increases its similarity to two overlapping reading frames in Escherichia coli.

An open reading frame (orfx) in mitochondria of the higher plants Oenothera berteriana and Arabidopsis thaliana is homologous to orf244 in the mitochondrial genome of Marchantia polymorpha. Homologous sequences are also present in carrot, potato and sugar beet. Profile analysis revealed similarity to two overlapping reading frames in the Escherichia coli genome. Potential translation initiation at conserved ATA (isoleucine) and TTG (leucine) codons is discussed. Transcripts of the open reading frame are altered by RNA editing in Arabidopsis and Oenothera downstream of these codons, suggesting this to be the functionally important region.

Amino Acid Sequence↗

PubMed1993

The mitochondrial genome on its way to the nucleus: different stages of gene transfer in higher plants.

The vast majority of mitochondrial proteins are in all eukaryotes encoded in the nuclear genomes by genes which have been transferred from the original endosymbiont. DNA as well as RNA was and is exchanged between organelles. A functionally successful information transfer, however, requires complex structural and regulatory alterations of the concerned gene. The recently identified variations of the information content in mitochondrial genomes of different plant species represent different stages of the transfer process. These evolutionary intermediates allow a definition of requirements and chances of successful gene transfers.

Cell Nucleus↗

PubMed1992

The nad4L gene is encoded between exon c of nad5 and orf25 in the Arabidopsis mitochondrial genome.

In the Arabidopsis thaliana mitochondrial genome the gene coding for subunit 4L of NADH dehydrogenase (nad4L) is located between exon c of the nad5 open reading frame and orf25. The physical proximity of these genes further supports the trans-splicing model for assembly of the nad5 mRNA. Some transcripts comprise the nad4L open reading frame cotranscribed with nad5 exon c and orf25, while other mRNAs contain only nad4L and orf25. Both open reading frames for nad4L and orf25 are edited in several positions with different frequencies.

Amino Acid Sequence↗

PubMed1991

Nucleotide sequences of the mitochondrial genes trnS(TGA) encoding tRNA(TGASer) in Oenothera berteriana and Arabidopsis thaliana.

The genes encoding tRNA(TGASer) have been investigated in the mitochondrial (mt) genomes of Oenothera berteriana and Arabidopsis thaliana. Sequence analysis shows four nucleotide (nt) differences between the two dicots, but only two differences between each dicot and the available monocot sequences. Similarity comparisons identify these genes as encoding a native mt tRNA(TGASer), with less than 77% of the nt identical to the corresponding chloroplast tRNAs.

Base Sequence↗

PubMed1991

Trans splicing integrates an exon of 22 nucleotides into the nad5 mRNA in higher plant mitochondria.

The genes coding for NADH dehydrogenase subunit 5 (nad5) in mitochondria of the higher plants Oenothera and Arabidopsis are split into five exons that are located in three distant genomic regions. These encode exons a + b, c and d + e, respectively. Maturation of the mRNAs requires two trans splicing events to integrate exon c of only 22 nucleotides. Both trans splicing reactions involve mitochondrial group II intron sequences that allow base pairings in the interrupted domain IV, demonstrating the flexibility of intron structures. The observation of fragmented intron sequences in plant mitochondria suggests that trans splicing is more widespread than previously assumed. RNA editing by C to U alterations in both Oenothera and Arabidopsis open reading frames improves the evolutionary conservation of the encoded polypeptides. Three C to U RNA editing events were observed in intron sequences.

Amino Acid Sequence↗

PubMed1991

Distribution of RNA editing sites in Oenothera mitochondrial mRNAs and rRNAs.

To investigate whether RNA editing in plant mitochondria modifies structural RNAs as well as protein-coding RNAs we compared the genomic-encoded information with the respective transcripts of several genes in Oenothera. The genes analysed are the 5S, 18S and 26 S rRNAs, the alpha-subunit of ATPase (atpA), cytochrome b (cytb), orfB, which is located upstream of cytochrome oxidase subunit III, and the respective leader, trailer and spacer sequences. All open reading frames were found to be edited to some degree. The atpA coding region has the least edited mRNA in Oenothera mitochondria, with only four nucleotides altered in the 1533 nucleotide open reading frame. From this analysis we conclude that frequent RNA editing is indicative of functional protein coding regions in plant mitochondria. The extensive editing in orfB, for example, suggests that this orf codes for a mitochondrial protein. No RNA editing event was found in the 5S rRNA or in the 1824 nucleotides analysed of the 18S rRNA, but two nucleotides were found to be altered in the 1970 nucleotides compared for the 26S rRNA. One nucleotide alteration has changed C to U, the other in reverse U to C. However, only one of five cDNA clones covering this region shows the modifications, similar to many silent editing events in open reading frames. RNA editing in the structural RNAs thus does not seem to be essential for their function in the mitochondrial ribosome.

Adenosine Triphosphatases↗

PubMed1991

A mitochondrial intron sequence in the 5'-flanking region of a plant nuclear lectin gene.

A sequence fragment from the cis-splicing intron between exons a and b of the NADH-dehydrogenase subunit 5 gene (nad5) in plant mitochondria is also present in one of two closely related nuclear-encoded lectin genes of Dolichos biflorus. This sequence of 116 nucleotides is the major difference in the 5'-flanking region of two recently described lectin genes (Harada et al. 1990). The stem and leaf lectin DB58 does not contain the insert, while the otherwise more than 90% identical 5'-flanking region of the seed lectin is interrupted by this mitochondrial intron sequence.

Base Sequence↗

PubMed1991

Expression of the avirulence gene avrBs3 from Xanthomonas campestris pv. vesicatoria is not under the control of hrp genes and is independent of plant factors.

The avirulence gene avrBs3 from Xanthomonas campestris pv. vesicatoria pepper race 1 is responsible for the induction of a race-specific hypersensitive reaction in resistant pepper cultivars. A DNA region of 3.7 kb, containing several open reading frames and an internal repetitive region, was shown previously to be necessary for avirulence activity (U. Bonas, R. E. Stall, and B. Staskawicz, Mol. Gen. Genet. 218:127-136, 1989). The promoter of avrBs3 was identified by using gene fusions to beta-glucuronidase. Also, we mapped the transcription start site and showed that the avrBs3 gene is expressed constitutively in cells grown in minimal or complex medium and in planta. Polyclonal antibodies raised against a fusion protein produced in Escherichia coli allowed the identification of a 122-kDa protein in X. campestris pv. vesicatoria cells expressing the avrBs3 gene. The antibody is specific for AvrBs3 in X. campestris pv. vesicatoria cells but also recognizes homologous proteins in other pathovars of X. campestris. We found that AvrBs3 is localized intracellularly in X. campestris pv. vesicatoria and is mainly in the soluble fraction. The effect of mutations in the hrp gene cluster on the function of AvrBs3 was examined. Expression of AvrBs3 in X. campestris pv. vesicatoria grown in minimal or complex medium is independent of the hrp gene cluster that determines pathogenicity and hypersensitivity to X. campestris pv. vesicatoria. In the plant, however, the hrp genes are required for elicitation of a race-specific resistance response.

Amino Acid Sequence↗