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F Kempken

Publications and source records attributed to F Kempken.

28 records · Page 2Linked to original sources
PubMed1995

Analysis of silent RNA editing sites in atp6 transcripts of Sorghum bicolor.

We have observed numerous examples of silent or rare non-silent editing sites in the amino-extension and part of the conserved core of mitochondrial atp6 transcripts of Sorghum. In this region of the 1.4-kb atp6-2 mRNA (position 300 to 550) two editing sites, which alter the amino-acid sequence and occur in all cDNAs analysed, were already known, while nine others were found which are silent or occur in a few mRNAs only. Many aspects of RNA editing in the mitochondria of higher plants are still unknown. This includes the influence of genomic background or silent RNA editing. We were interested in the influence of nuclear and mitochondrial backgrounds on RNA editing. Previous preliminary results indicated the possibility of line-specific editing at silent sites. However, a more comprehensive approach gave no consistent evidence for such editing. These results are discussed with respect to their potential impact on the evolution of mitochondrial genes.

Base Sequence↗
PubMed1992

Conserved sequence blocks 5' to start codons of plant mitochondrial genes.

Three sequence blocks of 10-12 bp are conserved in sequence and order 5' to putative start codons of several higher-plant mitochondrial genes. At least 25 examples were found, primarily associated with coxII, atp6, and orf25, in monocotyledons and dicotyledons. The proximal block can be 9 bp from start codons, and the three blocks generally occur within 100 bp 5' of start codons. In three examples 5' termini of the blocks represent recombination breakpoints, resulting in conservation of the blocks in resultant configurations. The two proximal blocks can form a secondary structure motif. The occurrence of the blocks near start codons, and conserved sequence and order, is consistent with a possible role in translation initiation or regulation.

Base Sequence↗
PubMed1992

Sorghum mitochondrial atp6: divergent amino extensions to a conserved core polypeptide.

Sorghum mitochondrial atp6 occurs as one copy in the line Tx398 and as two copies in IS1112C. In IS1112C a repeated sequence diverged within the atp6 open reading frames. The two open reading frames (1137 bp, atp6-1; 1002 bp, atp6-2) share an identical conserved region of 756 bp but are flanked 5' by divergent extensions of 246 (atp6-1) or 381 bp (atp6-2). Tx398 carried only atp6-2. The breakpoint of the repeated sequence of the conserved core region corresponds to the amino acid sequence Ser-Pro-Leu-Asp, which is the amino terminus of the proteolytically processed yeast ATP6. The 5' extensions of atp6-1 and atp6-2 were similar to those of rice and maize, respectively. Each open reading is transcribed, however nuclear background influenced transcriptional patterns of atp6-2 in IS1112C.

Amino Acid Sequence↗
PubMed1992

Evolution of linear plasmids.

Linear plasmids are genetic elements commonly found in yeast, filamentous fungi, and higher plants. In contrast to all other plasmids they possess terminal inverted repeats and terminal bound proteins and encode their own DNA and RNA polymerases. Here we present alignments of conserved amino acid sequences of both the DNA and RNA polymerases encoded by those linear plasmids for which DNA sequence data are available. Additionally these sequences are compared to a number of polymerases encoded by related viral and cellular entities. Phylogenetic trees have been established for both types of polymerases. These trees appear to exhibit very similar subgroupings, proving the accuracy of the method employed.

Amino Acid Sequence↗
PubMed1991

RNA editing of sorghum mitochondrial atp6 transcripts changes 15 amino acids and generates a carboxy-terminus identical to yeast.

Sequencing of sorghum mitochondrial atp6 cDNA clones revealed 19 C-to-U transcript editing events within a 756 bp-conserved core gene; three were silent and 16 resulted in 15 amino acid changes. Only one edit, which was silent, was found in the 381 bp amino-extension to the core gene. Eleven of the 15 changed amino acids were identical with or else represented conservative changes compared to yeast atp6. Editing of a CAA codon to TAA truncates the carboxy-terminus to a position identical to that of yeast. The frequency of editing at sites which change amino acids was very high in contrast to partial editing at silent, third base, sites.

Base Sequence↗
PubMed1991

Editing of mitochondrial atp9 transcripts from two sorghum lines.

Genomic and cDNA sequences of the ATP synthase complex subunit 9 (atp9) genes from two sorghum lines were determined. Sequences of cDNAs revealed eight C to U transcript editing events resulting in six amino acid changes and a new stop codon which eliminated 12 carboxy-terminal residues, compared to the genomic sequence. Sorghum atp9 has a unique five-residue amino-extension relative to other higher plants. The resulting predicted 79-residue gene product has a molecular weight of 8.179 kDa. The predicted phe-val-phe carboxy-terminus is identical to that from cDNA sequences of wheat, Oenothera, and petunia. Partial editing of transcripts was detected in each sorghum line.

Amino Acid Sequence↗
PubMed1989

In organello replication and viral affinity of linear, extrachromosomal DNA of the ascomycete Ascobolus immersus.

Linear, extrachromosomal DNA's of the filamentous fungus Ascobolus immersus are localized within the mitochondria. These linear plasmids have no homology to the high molecular weight mtDNA (hmw mtDNA). For analysis of plasmid replication an in organello DNA synthesis system was developed, in which radionucleotides were incorporated into intact mitochondria. Plasmid DNA is labelled preferentially in this system. From replication analysis of a specific plasmid there is evidence of a virus-like protein-primed replication. Sequence analysis of this plasmid reveals that a viral DNA polymerase is encoded. Thus, these genetic elements presumably are viral remnants rather than true plasmids.

Amino Acid Sequence↗
PubMedDate not supplied

A unique two-gene gametophytic male sterility system in sorghum involving a possible role of RNA editing in fertility restoration.

The sorghum line IS1112C carries a male sterility-inducing cytoplasm when introduced into nuclear backgrounds that do not include fertility restoration genes. An mtDNA chimeric configuration resulting from recombination/duplication with atp9 resulted in the formation of orf107, a chimeric open reading frame. Transcription of orf107 is driven by three promoters, and abundant whole-length transcripts are detected in male-sterile lines. Fertility restoration is exacted through a unique two-gene gametophytic system requiring complementary action of genes designated Rf3 and Rf4. In male-sterile lines carrying Rf3, or lines restored to fertility, an enhanced nucleolytic transcript processing activity is targeted within orf107, cleaving 75% of whole-length transcripts. Rf3 thus confers or regulates the nucleolytic processing activity. A correlation between the frequency of RNA editing at two sites in orf107 and transcript processing suggests that processing may be dependent on templates edited at these sites. In addition, editing of atp6 transcripts is specifically reduced in anthers/pollen of male-sterile lines. Partially restored F1s and segregating F2s exhibit atp6 editing frequencies consistent with the possibility that Rf4 may confer the restitution of normal editing frequency. Thus RNA editing may be involved in features of fertility restoration in this unusual system.

Amino Acid Sequence↗