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T D Fox

Publications and source records attributed to T D Fox.

83 records · Page 5Linked to original sources
PubMed1981

The Zea mays mitochondrial gene coding cytochrome oxidase subunit II has an intervening sequence and does not contain TGA codons.

Cross hybridization between maize mitochondrial DNA fragments and a specific yeast mitochondrial DNA probe from the oxi 1 gene has been used to identify and isolate the maize mitochondrial gene coding cytochrome oxidase subunit II, mox 1. The DNA sequence reveals two coding regions separated from each other by a single centrally located intervening sequence. Hybridization of mox 1 DNA probes to mitochondrial RNA from plants shows that te gene is transcribed and indicates that several transcripts are spliced. TGA codons, which code Trp in the mitochondria of all species examined to date, do not occur in this gene. However, alignment of the mox 1 gene sequence with the amino acid sequences of subunit II from other organisms strongly suggests that codon CGG (normally Arg) codes for Trp in maize mitochondria, in addition to the standard Trp codon TGG.

Base Sequence↗
PubMed1980

Leaky +1 and -1 frameshift mutations at the same site in a yeast mitochondrial gene.

Two mutations in a mitochondrial structural gene, which cause leaky premature polypeptide chain termination and leaky growth, are +1 and -1 frameshifts in the same run of five T residues. The partial restoration of reading frame is probably due to ribosomal frameshifting at this site, and may be promoted by the unique structure of the yeast mitochondrial t RNAPhe.

DNA, Mitochondrial↗
PubMed1979

Five TGA "stop" codons occur within the translated sequence of the yeast mitochondrial gene for cytochrome c oxidase subunit II.

A mitochondrial mutation that genetically maps in the middle of the gene coding cytochrome c oxidase subunit II has been found to be a single-base-pair deletion. Three independently isolated spontaneous revertants of this mutant have different single-base-pair insertions within 15 nucleotides of the mutation. These findings clearly identify the location of the gene and suggest that the mutation causes a frame-shift. The sequence of about 900 base pairs surrounding the mutation has been determined and found to have several chain termination codons in every possible reading frame. The sequence can, however, be translated in one frame by assuming that the codon TGA does not cause chain termination in yeast mitochondira, as was recently suggested for the human organelle [Barrell, B. G., Bankier, A. T. & Drouin, J. (1979) Nature (London), in press]. If TGA codes for tryptophan residues, as is apparently the case in human mitochondria, a polypeptide can be read from the yeast mtDNA that is identical to bovine cytochrome oxidase subunit II at 37.8% of its residues. Furthermore, the DNA sequences of the frame-shift revertants discussed above predict relative isolectric point differences between the wild-type and various revertant forms of the polypeptide. The detection of these isolectric point differences by two-dimensional electrophoresis of subunit II from the various strains independently confirms the presumed reading frame of the gene. It is concluded that TGA is translated in yeast mitochondria, most probably as tryptophan.

Base Sequence↗
PubMed1975

Highly asymmetric transcription by RNA polymerase containing phage-SP01-induced polypeptides and a new host protein.

An RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) has been purified from phage-SP01-infected Bacillus subtilis that copies RNA almost exclusively from the heavy strand of native SP01 DNA, the DNA strand from which "middle" and "late" classes of RNA are copied in vivo. Hybridization-competition established that this RNA polymerase termed enzyme A, preferentially synthesizes middle RNA in vitro. Enzyme A contains beta',beta, alpha, and two newly identified host polypeptides, variation of (21,500 daltons) and omega (11,000 daltons). All of these polypeptides are associated with highly purified RNA polymerase from uninfected bacteria. In addition, enzyme A contains phage-induced subunits of 26,000, 24,000, and 13,500 daltons. Enzyme A lacks sigma polypeptide, and strand-selective transcription by this enzyme is resistant to anti-sigma antibody. A reconstitution experiment strongly suggests that the host variation of protein is required in addition to a phage-induced subunit(s) (or an unidentified phage-induced modification) for strand-selective transcription of SP01 middle genes in vitro.

Bacillus subtilis↗
PubMed1974

New phage-SPO1-induced polypeptides associated with Bacillus subtilis RNA polymerase.

RNA polymerase was precipitated from extracts of Bacillus subtilis infected with phage SP01 by antiserum prepared against core RNA polymerase. As shown by sodium dodecyl sulfate gel electrophoresis, the precipitates contained at least five new polypeptides not present in uninfected bacteria, in addition to the known subunits of RNA polymerase. The molecular weights of these polypeptides are (1) 85,000; (II) 40,000; (III) 28,000; (IV) 25,000; and (V) 23,000. Four of the polypeptides (I, III, IV, and V) co-purified with RNA polymerase through gel filtration and phosphocellulose chromatography. A pulse-chase experiment indicated that all five polypeptides are synthesized de novo after infection. The synthesis of polypeptides II, III, and IV commences almost immediately after infection, while polypeptides I and V first appear several minutes later. A sus mutant blocked early in transcription, susF21 [Fujita, et al. (1971) J. Mol. Biol. 57, 301-317] failed to induce polypeptides I, IV, and V, while two other mutants, susF4 and susF14, blocked late in transcription both failed only to induce polypeptide V.

Animals↗
PubMedDate not supplied

Relocation of the unusual VAR1 gene from the mitochondrion to the nucleus.

The Var1 protein (Var1p) is an essential, stoichiometric component of the yeast mitochondrial small ribosomal subunit, and it is the only major protein product of the mitochondrial genetic system that is not part of an energy transducing complex of the inner membrane. Interestingly, no mutations have been reported that affect the function of Var1p, presumably because loss of a functional mitochondrial translation system leads to an instability of mtDNA. To study the structure, function and synthesis of Var1p, we have engineered yeast strains for the expression of this protein from a nuclear gene, VAR1U, in which 39 nonstandard mitochondrial codons were converted to the universal code. Immunoblot analysis using an epitope-tagged form of Var1Up showed that the nuclear-encoded protein was expressed and imported into the mitochondria. VAR1U was tested for its ability to complement a mutation in mtDNA, PZ206, which disrupts '3-end processing of the VARI mRNA, causing greatly reduced synthesis of Var1p and a respiratory-deficient phenotype. Respiratory growth was restored in PZ206 mutants by transformation with a centromere plasmid carrying VAR1U under ADH1 promoter control, thus proving that VAR1 function can be relocated from the mitochondrion to the nucleus. Moreover, epitope-tagged Var1Up co-sedimented specifically with small ribosomal subunits in high salt sucrose gradients. The relocation of VAR1 from the mitochondrion to the nucleus provides an excellent system for the molecular genetic analysis of structure-function relationships in the unusual Var1 protein.

Base Sequence↗