Mitochondrial translation products of yeast mutants resistant to mucidin

Analysis by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate of the mitochondrially translated polypeptides of mucidin-resistant mutantsmuc1, muc2 andmuc3 failed to reveal any modification in the electrophoretic mobility of apocytochromeb coded for by sequences of mitochondrial DNA comprising these mutations.     

Mitochondrial mutants of the yeast Saccharomyces cerevisiae showing resistance in vitro to chloramphenicol inhibition of mitochondrial protein synthesis

Two cytoplasmic genetic mutants of yeast, genetically separable by recombination, displaying high levels of chloramphenicol resistance have been isolated. Protein synthesis in isolated mitochondria of mutant [$\text{cap 2-r}$] is almost completely resistant to chloramphenicol inhibition while that in mitochondria of mutant [$\text{cap 1-r}$] is partially resistant. Biochemical differences between the two mutants were confirmed by studies of chloramphenicol inhibition of aerobic adaptation of anaerobically grown cells. The mutants appear to contain altered mitochondrial ribosomes.     

New antibiotic resistance Loci in the ribosomal region of yeast mitochondrial DNA

A large number of mitochondrial antibiotic-resistant mutants have been isolated following mutagenesis with manganese. These include several different phenotypic classes of mutants, as distinguished by cross-resistance patterns, that have been found to be allelic at cap1 or ery1; some have been found to be heteroallelic.--Seven chloramphenicol-resistant mutants have been identified that are nonallelic by recombination tests with the three loci (cap1, spi1 and ery1) previously identified in the ribosomal region. Four of these are allelic with each other and define a new locus, cap3; two others are allelic and define another new locus, cap2; the seventh maps at yet a different locus, cap4. One new spiramycin-resistant mutant has been identified that defines still another new locus, spi2. A variety of genetic techniques have been used to map these loci within the ribosomal region of the mitochondrial genome.-Manganese has been shown to be effective in inducing the mutation from omega(-) to omega(n) in many mutants that experience a simultaneous mutation at the closely linked cap1 locus. The omega(n) mutation has also been described in the cap4 mutant, and this locus has been shown to be more closely linked to omega than cap1 is to omega.     

Search for ribosomal mutants in Podospora anserina: Genetic analysis of mutants resistant to paromomycin

It has recently been shown that paromomycin, an antibiotic of the aminoglycoside family, is also active on eukaryotic cytoplasmic ribosomes. In the fungus Podospora anserina, genetic analysis of ten mutants resistant to high doses of paromomycin shows that this resistance is caused by mutations in two different nuclear genes. These mutants display pleiotropic phenotypes (cold sensitivity, mycelium and spore appearance and coloration, cross-resistance to other antibiotics). Double mutants are either lethal or very altered and unstable. Moreover, the cytochrome spectra of these mutants seem to indicate that cytoplasmic protein synthesis is affected. The mutants also display a slight suppressor effect. We can therefore assume that these mutations affect cytoplasmic ribosomes.This work was supported by a C.N.R.S. Grant (ATP Microbiologie No. 3052) and by a NATO Grant.     

Erythromycin and spiramycin resistance mutations of yeast mitochondria: nature of the rib2 locus in the large ribosomal RNA gene.

Two linked genetic loci, rib 2 and rib 3, of yeast mitochondrial genome are the sites of mutations that confer resistance to erythromycin and/or spiramycin. We have examined two mutations at the rib 2 locus. Mutation ER354 was found at the nucleotide position 3993 of the large ribosomal RNA gene; it corresponded to a C to G transversion leading to a double resistance to erythromycin and spiramycin. Mutation SR551 was found also at the same position, but the C was replaced by a T, conferring resistance to spiramycin only. Rib 2 and rib 3 are 836 base pairs apart on the gene sequence, but are very close to each other in the secondary structure of ribosomal RNA.     

Biochemical and genetic studies on two different types of erythromycin resistant mutants of Escherichia coli with altered ribosomal proteins

Summary Ribosomes from nine E. coli mutants with high level resistance to the antibiotic erythromycin were isolated and their proteins were compared with those of the parental strains by two-dimensional polyacrylamide gel electrophoresis, by carboxymethylcellulose column chromatography and by immunological techniques. Two 50S proteins were found to be altered in the mutants: either L 4 or L 22.Ribosomes with an altered L4 protein bound erythromycin rather poorly and the formation of N-acetylphenylalanyl puromycin was drastically decreased. On the other handribosomes with an altered L22 protein bound erythromycin as efficiently as wild type ribosomes and their puromycin reaction was at least as good as that of wild type ribosomes.Transduction experiments showed that the mutations affecting both proteins, L4 and L22, are located very close to the str and spc genes, nearer to the spc than to str gene.Paper No. 61 on Ribosomal Proteins. Preceding paper is by Hasenbank et al., Molec. gen. Genet., 127, 1–18 (1973).Communicated by E. Bautz     

Alteration of 23 S ribosomal RNA and erythromycin-induced resistance to lincomycin and spiramycin in Staphylococcus aureus

Functionally active “hybrid” 50 S ribosomal subunits can be reconstituted using 23 S RNA from Staphylococcus aureus (strain 1206) and 5 S RNA, as well as 50 S ribosomal proteins from Bacillus stearothermophilus. Using this system, resistance of S. aureus 50 S subunits to lincomycin and spiramycin was analyzed. When 23 S RNA from either phenotypically resistant (“induced resistance”) S. aureuscells or derived genetically resistant (“constitutive resistance”) S. aureus cells, were used, the reconstituted 50 S subunits showed the resistant phenotype similar to that seen in native 50 S subunits obtained from resistant cells; only very weak inhibition by the antibiotics was observed in poly (U) - directed polyphenylalanine synthesis involving these 50 S subunits. In contrast, the 50 S particles reconstituted using 23 S RNA from uninduced (sensitive) S. aureus were subject to greater inhibition by the antibiotics in cell-free poly-peptide synthesis. It is concluded that modification of 23 S RNA, presumably the previously observed methylation to form dimethyladenine, is responsible for the resistance to the antibiotics in this strain of S. aureus.     

Isolation of Chinese hamster ovary ribosomal mutants differentially resistant to ricin, abrin, and modeccin

The molecular action of ricin A chain involves cleavage of the N-glycosidic bond between ribose and the adenine 4324 nucleotides from the 5' end of mammalian 28 S rRNA (Endo, Y., and Tsurugi, K. (1987) J. Biol. Chem. 262, 8128-8130). In this paper, four ricin- and abrin-resistant Chinese hamster ovary cell mutants that possess ribosomes resistant to this N-glycosidase action are described. Three of the mutant phenotypes, Lec26, Lec27, and Lec28, were recessive in somatic cell hybrids and define at least two new lectin-resistant complementation groups. The most extensively characterized mutant type, LEC17, was dominant in such hybrids. None of the mutants were cross-resistant to modeccin. Post-mitochondrial supernatants from each of the four mutants were resistant to inhibition of cell-free protein synthesis by ricin, ricin A chain, and abrin. In addition, polysomes isolated from mutant cells were resistant to cleavage of the adenine-ribose N-glycosidic bond by ricin A chain or abrin, as assayed by the release of an approximately 470-nucleotide fragment following aniline treatment of ribosomal RNA extracted from toxin-treated polysomes. The unique lectin-resistance properties of the different mutants suggests that the accessibility of adenine 4324 to each toxin differs. It seems likely that the recessive Chinese hamster ovary ribosomal mutants reflect structural changes in different ribosomal proteins while the dominant phenotype may be due to the modification of protein(s) or rRNA involved in toxin-ribosome interaction. Further analysis of these cell lines should provide new insights into the structure/function relationships of eukaryotic ribosomes.     

Improved properties of baker's yeast mutants resistant to 2-deoxy-D-glucose

We isolated spontaneous mutants from Saccharomyces cerevisiae (baker's yeast V1) that were resistant to 2-deoxy-D-glucose and had improved fermentative capacity on sweet doughs. Three mutants could grow at the same rate as the wild type in minimal SD medium (0.17% Difco yeast nitrogen base without amino acids and ammonium sulfate, 0.5% ammonium sulfate, 2% glucose) and had stable elevated levels of maltase and/or invertase under repression conditions but lower levels in maltose-supplemented media. Two of the mutants also had high levels of phosphatase active on 2-deoxy-D-glucose-6-phosphate. Dough fermentation (CO2 liberation) by two of the mutants was faster and/or produced higher final volumes than that by the wild type, both under laboratory and industrial conditions, when the doughs were supplemented with glucose or sucrose. However, the three mutants were slower when fermenting plain doughs. Fermented sweet bakery products obtained with these mutants were of better quality than those produced by the wild type, with regard to their texture and their organoleptic properties.     

Identification of two erythromycin resistance mutations in the mitochondrial gene coding for the large ribosomal RNA in yeast

Two independent erythromycin resistance mutations, ER514 and ER221, have been identified in the mitochondrial gene coding for the 21S ribosomal RNA. The two mutations were found to be identical, corresponding to a A to G transition at the nucleotide position 1951 of the ribosomal RNA gene. In the secondary structure model of the ribosomal RNA, the ER resistance site is found at the proximity of the chloramphenicol resistance sites located about 500 bases downstream.     

Mitochondrial DNA replication in petite mutants of yeast: Resistance to inhibition by ethidium bromide, berenil and euflavine

Summary Mitochondrial DNA (mtDNA) replication in petite mutants ofSaccharomyces cerevisiae is generally less sensitive to inhibition by ethidium bromide than in grande (respiratory competent) cells. In every petite that we have examined, which retain a range of different grande mtDNA sequences, this general phenomenon has been demonstrated by measurements of the loss of mtDNA from cultures grown in the presence of the drug. The resistance is also demonstrable by direct analysis of drug inhibition of mtDNA replication in isolated mitochondria. Furthermore, the resistance to ethidium bromide is accompanied, in every case tested, by cross-resistance to berenil and euflavine, although variations in the levels of resistance are observed.In one petite the level of in vivo resistance to the three drugs was very similar (4-fold over the grande parent) whilst another petite was mildly resistant to ethidium bromide and berenil (each 1.6-fold over the parent) and strongly resistant (nearly 8-fold) to inhibition of mtDNA replication by euflavine. The level of resistance to ethidium bromide in several other petite clones tested was found to vary markedly. Using genetic techniques it is possible to identify those petites which display an enhanced resistance to ethidium bromide inhibition of mtDNA replication.It is considered that the general resistance of petites arises because a product of mitochondrial protein synthesis is normally involved in facilitating the inhibitory action of these drugs on mtDNA synthesis in grande cells. The various levels of resistance in petites may be modulated by the particular mtDNA sequences retained in each petite.     

Peptide analyses of a protein component, 50-8, of 50s ribosomal subunit from erythromycin resistant mutants of Escherichia coli and Escherichia freudii

Summary Chromatographic analyses on a Dowex 50x8 column of tryptic digests of the mutationally altered 50-8 protein component from several erythromycin resistant (ery ^r) mutants of Escherichia coli and Escherichia freundii have been performed. It was found that (1) the difference in the elution profile of the altered components detected with carboxymethyl cellulose column chromatography reflects the difference in their amino acid sequence, (2) the structural change(s) of the 50-8 protein from three E. coli ery ^r mutants examined seems to exist only in the same single peptide fragment and (3) the primary structure of the 50-8(R) protein of E. freundii (ery ^s: wild type) differs from that of E. coli Q13 (ery ^s) and the structural change in 50-8(R) component of E. freundii caused by the ery ^r mutation was found to take place in different peptide fragments from that in which the mutational change of the E. coli 50-8 component occurred.