Biomedical subjects

D F Spencer

Publications and source records attributed to D F Spencer.

22 records · Page 2Linked to original sources

PubMed1981

Is wheat mitochondrial 5S ribosomal RNA prokaryotic in nature?

Küntzel et al. (1981) (Nucleic Acids Res. 9, 1451-1461) recently concluded that the sequence of wheat mitochondrial 5S rRNA is significantly more related to prokaryotic than to eukaryotic 5S rRNA sequences, and displays an especially high affinity to that of the thermophilic Gram-negative bacterium, Thermus aquaticus. However, the sequence on which this conclusion was based, although attributed to us, differs in several places from the one determined by us. We show here that the correct sequence (Spencer, D.F., Bonen, L. and Gray, M.W. (1981) Biochemistry, in press) does not support the conclusions of Küntzel et al. about potential secondary structure in wheat mitochondrial 5S rRNA and its phylogenetic significance. We further show that when the wheat mitochondrial 5S rRNA sequence is matched against published alignments for E. coli, T. aquaticus, and wheat cytosol 5S rRNAs, the mitochondrial sequence shows no greater homology to the T. aquaticus sequence than to the E. coli sequence, and only slightly more homology to these two sequences than to wheat cytosol 5S rRNA. This analysis confirms our original view (Biochemistry, in press) that wheat mitochondrial 5S rRNA is neither obviously prokaryotic nor eukaryotic in nature, but shows characteristics of both classes of 5S rRNA, as well as some unique features.

Base Sequence↗

PubMed1981

Primary sequence of wheat mitochondrial 5S ribosomal ribonucleic acid: functional and evolutionary implications.

Using the procedures of Donis-Keller et al. [Donis-Keller, H., Maxam, A. M., & Gilbert, W. (1977) Nucleic Acids Res. 4, 2527--2538 (1977)] and Peattie [Peattie, D. A. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 1760--1764], we have determined the nucleotide sequence of wheat mitochondrial 5S ribosomal ribonucleic acid (rRNA). This sequence [Formula: see text] is the first to be reported for a plant mitochondrial RNA. A highly conserved region (underlined) readily identifies the molecule as a structural homologue of other 5S rRNAs, as do potential base-paired regions which are characteristic of all known (prokaryotic, chloroplast, eukaryotic cytosol) 5S rRNA sequences. However, when assessed in terms of those structural features which distinguish prokaryotic from eukaryotic 5S rRNAs, wheat mitochondrial 5S rRNA cannot be classified readily as one or the other but instead displays characteristics of both types. In addition, the mitochondrial 5S rRNA has several unusual features, including (i) a variable number (two to three) of A residues at both the 5' and 3' ends, (ii) a unique sequence (CGACC, italic) in place of the prokaryotic sequence (CGAAC) which has been postulated to interact with aminoacyl-tRNA during translation, and (iii) a novel sequence, AUAUAUAU, immediately following the highly conserved sequence. In terms of overall primary sequence, wheat mitochondrial and cytosol 5S rRNAs seem to be slightly more divergent from each other than either is from Escherichia coli 5S rRNA, with which they are about equally homologous. From these observations, we propose that wheat mitochondrial 5S rRNA represents a distinct class of 5S rRNA. Our observations raise a number of questions about the evolutionary origin and functional role(s) of plant mitochondrial 5S rRNA.

Base Composition↗

PubMed1980

Nucleotide sequences of wheat-embryo cytosol 5-S and 5.8-S ribosomal ribonucleic acids.

The nucleotide sequences of wheat embryo 5.8-S and 5-S rRNAs have been determined with the use of several techniques, including classic analysis of oligonucleotides generated by ribonuclease T1 and resolution on gels of terminally labelled RNA partially degraded with ribonucleases or with chemical reagents. The sequence of wheat embryo 5.8-S rRNA was found to be (formula: see text). This sequence is compared to 5-S rRNA sequences previously published for wheat and several other angiosperms.

Base Sequence↗

PubMed1979

Indirect and intragenic suppression of the lexA102 mutation in E. coli B/r.

In Escherichia coli B/r the expression of UV inducible (SOS) functions is under the control of the recA and lexA genes. In this study we have characterized mutants which are altered in their ability to express SOS functions. These mutants were isolated as UV resistant UV nonmutable (Rnm) derivatives of the lexA102 uvrA155 mutant strain WP51. The UV resistance of these Rnm strains is a result of the suppression of lexA102 mediated UV sensitivity. Genetic mapping of rnm mutations shows that the two predominant classes, rnmA and rnmB, map in or very near the lexA and recA genes respectively. rnmA mutations differ from rnmB with regard to recA protein synthesis, rnmA mutations do not restore the ability to express high levels of recA protein after UV treatment whereas rnmB mutations result in constitutive expression of high levels of recA protein. However, both rnmA and rnmB mutant strains inhibit postirradiation DNA degradation. This shows that in rnmA strains, high levels of recA protein are not needed to inhibit postirradiation DNA degradation. The genetic map location and constitutive expression of recA protein synthesis resulting from rnmB mutations suggests that they are operator constitutive mutations of the recA gene. The result that the lexA+ gene is required for the expression of UV mutagenesis in rnmB mutants shows that high levels of recA protein do not circumvent the need for the lexA+ gene product in this process. Thus, while the lexA gene product is required for the induction of recA protein synthesis, lexA must have an additional role in UV induced mutagenesis.

Bacterial Proteins↗