Analysis of rpsD mutations in Escherichia coli. I. Comparison of mutants with various alterations in ribosomal protein S4.

Summary Streptomycin-independent revertants were selected from streptomycin-dependent mutants. Twenty-five out of 150 such revertants were temperature sensitive. Ribosomal proteins from 18 temperature-sensitive and 10 temperature-insensitive revertants were analysed by SDS-polyacrylamide gel electrophoresis. Seventeen of the former but none of the latter category showed an alteration of protein S4. The mutated rpsD allele of 6 temperature-sensitive revertants was transduced into a rpsL ⁺ strain. In all cases an increased suppressibility of T4 amber phages was observed. Such suppressibility was not observed in the original rpsD, rpsL strains. All 18 temperature-sensitive mutants were disturbed in the processing of 17s to 16s RNA at non-permissive temperature and the accumulated 17s RNA was degraded. Temperature-insensitive rpsD revertants could be isolated, which had gained a second alteration in S4. Such revertants, which had lost the temperature-sensitive property, were also unable to suppress growth of T4 amber phages.It is concluded that temperature-sensitive growth, inability to process 17s RNA and to assemble 30S ribosomes at non-permissive temperature as well as increased translational ambiguity are highly correlated properties in rpsD mutants.     

Improved Inosine Production and Derepression of Purine Nucleotide Biosynthetic Enzymes in 8-Azaguanine Resistant Mutants of Bacillus subtilis

Improved inosine producers were found with a high frequency among the mutants resistant to a low concentration of 8-azaguanine derived from AMP deaminase negative adenine auxotrophs of Bacillus subtilis K strain. The best mutant accumulated 16~18 g/liter of inosine, 60~80% higher than the parent. PRPP amidotransferase and succino-AMP lyase of all of the improved inosine producers tested were not repressed by adenosine but still repressed by guanosine. Adenine permeability was suggested to be also altered in some of the mutants which produced inosine even in the presence of a high concentration of adenine. Adenine prototrophic revertants from all of the mutants tested accumulated a small amount of adenosine but not inosine.     

Characterization of revertants of stmF mutants of Dictyostelium discoideum: Evidence that stmF is the structural gene of the cgmp-specific phosphodiesterase

stmF mutants of Dictyostelium discoideum produce long, banded aggregation streams on growth plates and exhibit altered cGMP metabolism. To learn more about the role of cGMP in chemotaxis and the nature of the defect in these mutants, 15 nonstreaming (Stm⁺) revertants of two stmF mutants were isolated and characterized. Fourteen of the revertants continued to show the elevated cAMP-induced cGMP response and very low cGMP-specific phosphodiesterase (cGPD) activity characteristic of their stmF parents. Parasexual genetic analysis revealed that many of these Stm⁺ revertants carried phenotypic suppressors unlinked to stmF. One Stm⁺ revertant, strain HC344, exhibited a low, prolonged cGMP response and relatively high cGPD activity throughout development. To determine whether the elevated cGPD activity in this revertant resulted from increased enzyme production or enhanced enzyme activity, cGPDs were partially purified from the wild-type strain, the stmF parent and revertant HC344, and properties of the enzymes were compared. cGPDs from the stmF mutant and the revertant showed similar differences from the wild-type enzyme in kinetic properties, thermal stability, and sensitivity to certain inhibitors. These results suggest that stmF is the structural gene of the cGPD. In addition, the unusual cGMP response in revertant HC344 appeared to be due to increased production of an altered cGPD.     

A spectinomycin dependent mutant of Escherichia coli.

Summary A mutant of Escherichia coli B has been isolated which shows a novel phenotype of spectinomycin dependence. The mutant, termed RD, needs spectinomycin to grow at temperatures of 37° or below; it is unable to grow at 42° in either the presence or absence of spectinomycin. Secondary mutants which grow well in the absence of spectinomycin can be isolated spontaneously at a frequency of about 10^-6. Two-dimensional gel electrophoresis of ribosomal proteins from 25 of these revertants showed that two revertants had an alteration in S4; one other showed an alteration in L5, and one showed an apparent absence of L1. Mutant RD itself had an altered less basic S5, which was maintained in all the revertants that were checked.Genetic analysis indicated that RD was a double mutant: one mutation, which alone conferred a spectinomycin resistant phenotype on the strain, was located in the strA region of the E. coli chromosome and was represented by the mutation in S5. The other mutation, which conferred the dependence on spectinomycin, mapped close to the rif locus.     

Revertants of selfing (gad) mutants in Physarum polycephalum

The conversion of the uninucleate amoebal form of Physarum polycephalum to the multi-nucleate plasmodial form is under the control of a genetic region which contains matA (or mt), a determinant of mating specificity. The region is the site of most gad mutations, which give amoebae the ability to produce plasmodia in clones without mating (ie, to self). In the present study, nonselfing revertants were isolated from two matA2-derived gad mutants and two matA3-derived gad mutants. Some revertants were found to have regained exactly, or nearly, the same phenotype as the original matA2 or matA3 strain. Others expressed new mating types, having gained the ability to mate with strains of the parental matA type. The results are compatible with a model in which new mating types arise from forward mutations (gad) and back mutations (npf or no plasmodium formation) occurring successively in a single gene, matA.     

Genetic determination of ploidy level in Xanthophyllomyces dendrorhous

Xanthophyllomyces dendrorhous (formely Phaffia rhodozyma) is a basidiomycetous yeast-like fungus that produces carotenoids useful for the food industry. Recently, its sexual cycle was reported but little is known about its genetic constitution. To inquire into the ploidy state of X. dendrorhous, biased mutant spectrum, genetic complementation and mitotic recombination analysis were used. A wild-type strain was subjected to N-methyl-N′-nitro-N-nitrosoguanidine mutagenic treatment. Auxotrophic and carotene mutants were forced to revert to the wild-type phenotype. Pigment producing and prototroph revertants behaved as diploid except for adenine less mutants. These results are in agreement with the limited spectrum of auxotrophs obtained in this strain for the ADE1 locus. To analyze the genetic characteristic of the adenine genetic marker of X. dendrorhous, protoplast fusion experiments with several adenine less mutants were performed. The experiments presented in this work suggest that the ATCC 2430 (UDC 67-385) strain of X. dendrorhous is diploid and a heterozygous constitution is proposed for the ADE1 locus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analogue-resistant and auxotrophic mutants ofMethanobacterium thermoautotrophicum

The death rate ofMethanobacterium thermoautotrophicum strain Marburg upon exposure toN-methyl-N-nitro-N-nitrosoguanidine under anaerobic conditions was of the same order of magnitude as the death rates that have been reported forEscherichia coli. Cultures of the methanogenic bacterium, mutagenized by nitrosoguanidine-treatment and grown under non-selective conditions, yielded mutants resistant toDL-ethionine (30 mM) or to 2-bromoethane sulfonic acid (3.8 mM). No mutants were observed in untreated controls. Among 1500 clones obtained from nitrosoguanidine-treated cell suspensions there were 6 mutants requiring a single growth factor each, namelyl-leucine,l-phenylalanine, thiamine (2 mutants) or adenosine (2 mutants). Three mutant-strains were studied in more detail. They were genetically stable (no revertants among 10⁹ cells), and wild type growth rates were restored by 5 mml-leucine, 0.4 mM adenosine and 0.03 mM thiamine, respectively.Abbreviations 2-BES 2-bromoethanesulfonic acid - MIC minimum inhibitory concentration     

Accumulation of Nucleic Acid-related Substances by Microorganisms

The induction of adenosine-producing mutants from an inosine-producing mutant previously derived from a Bacillus strain was attempted, and it was found out that the xanthine-requiring mutants lacking of adenase produce a large amount of adenosine.

The outline of the processes for the derivation of these mutants was described. Main product of these mutants was adenosine, and the culture broth contained a little amount of adenine as a by-product.

The culture conditions optimal for the production of adenosine were investigated, and the yield of adenosine in the culture broth was more than 16 mg/ml.     

Nucleotide sequence of dihydrofolate reductase genes from trimethoprim-resistant mutants of Escherichia coli. Evidence that dihydrofolate reductase interacts with another essential gene product

Summary We report the construction of recombinant plasmids containing the dihydrofolate reductase structural gene (fol) from several trimethoprim-resistant mutants of Escherichia coli. Strains carrying some of these plasmids produced approximately 6% of their soluble cell protein as dihydrofolate reductase and are therefore excellent sources of the purified enzyme for inhibitor binding or mechanistic studies. The nucleotide sequence of the fol region from each of the plasmids was determined. A plasmid derived from a K_i mutant which produced a dihydrofolate reductase with lowered affinity for trimethoprim contained a mutation in the structural gene that altered the sequence of the polypeptide in a conserved region which is adjacent to the dihydrofolate binding site. Two other independently-isolated mutants which overproduced dihydrofolate reductase had a mutation in the-35 region of the fol promoter. One of them, strain RS35, was also temperature-sensitve for growth in minimal medium. This phenotype was shown to be the result of an additional mutation in a locus unlinked to fol by P1 transduction. The fol regions from two temperature-independent revertants of strain RS35 were sequenced. One of these had a mutation within the dihydrofolate reductase structural gene which altered some properties of the enzyme. This confirmed some previous enzymological data which suggested that some revertants of strain RS35 had mutations in fol (Sheldon 1977). These results suggest that dihydrofolate reductase interacts physically with some other essential gene product in E. coli.     

Phenotypic reversion in some early blocked sporulation mutants of Bacillus subtilis. Genetic study of polymyxin resistant partial revertants

Summary A class of suppressor mutations restores, in pleiotropic sporulation mutants of B. subtilis (SPO mutants), the wild type level of resistance to Polymyxin, and, most often, other properties of the wild strain as well, but never the ability to sporulate. These suppressors, extracistronic, are active on mutations occurring in any one of the 5 genes in which SPO mutations have been found. The phenotype of the suppressed strains is dependent on both the suppressed (SPO) and the suppressive mutations. All these suppressors are located in a single locus and some of them are thermosensitive. The evidence suggests that a physiological compensation is at work in the partial revertants, so that the locus at which the suppressors are located was called cps X. Two hypotheses are discussed that might account for these observations.     

Genetic analysis of revertants for the nitrate reductase function of Nicotiana plumbaginifolia

Summary Spontaneous revertants of nitrate reductase (NR)-less mutants were isolated by screening for nitrate utilization in diploid NR^– protoplast cultures of Nicotiana plumbaginifolia. The revertants contained in vivo NR activity in the case of apoenzyme mutants (nia) as well as of a cofactor-deficient (cnx) mutant. Revertants of the NIA type proved to be tetraploid, and genetic analysis showed that only one out of the four NR structural genes had reverted to a functional allele.     

Cold-sensitive growth of a mutant of Escherichia coli with an altered ribosomal protein S8: analysis of revertants.

Summary 26 cold-resistant revertants of a cold-sensitiveEscherichia coli mutant with an altered ribosomal protein S8 were analyzed for their ribosomal protein pattern by two-dimensional polyacrylamide gel electrophoresis. It was found that 16 of them had acquired the apparent wild-type form of protein S8, one exhibits a more strongly altered S8 than the original mutant and two revertants regained the wild-type form of S8 and, in addition, possess alterations in protein L30. The ribosomes of the residual revertants showed no detectable difference from those of the parental S8 mutant.The mutation leading to the more strongly altered S8 was genetically not separable from the primary S8 mutation; this indicates that both mutations are very close to each other or at the same site. The structural gene for ribosomal protein L30 was mapped relative to two other ribosomal protein genes (for proteins S5 and S8) by the aid of one of the L30 mutants: The relative order obtained is:aroE....rpmD(L30)....rpsE(S5)....rpsH(S8)....THe L30 mutation impairs growth and ribosomal assembly at 20°C and is therefore the first example of a mutant with a defined 50S alteration that has (partial) cold-sensitive ribosome assembly. A double mutant was constructed which possesses both the S8 and the L30 mutations. It was found that the L30 mutation had a slight antagonistic effect on the growth inhibition caused by the S8 mutation. Thus the L30 mutants might have possibly arisen from the original S8 mutants first as S8/L30 double mutants which was followed by the loss of the original S8 lesion.     

Synthesis of different pectinases by filamentous growingA. niger mutants

Mutants ofA. niger K 69/26, prepared by multistep mutagenesis (UV, MNNG, heating) have been screened for pectinase activities. Mutants with altered levels of certain pectinases, such as endo- and exopolygalacturonase (PG vis, red), pectinesterase (PE) and pectinlyase (PL), were isolated. The enzyme activities of the best mutants M 1348/126 were increased 2–3-fold compared to the parent strain after a 6-d cultivation of filamentous mycelium on a shaker. Further mutagenesis of mutants with decreased pectinase activities (e.g. Se3) produced revertants. PG (vis) synthesis of revertant Se5 was increased 1.7 times compared to the control strain K 69/26. Independent of these increased rates, the general level of pectinase activities synthesized by the filamentous mycelium ofA. niger mutants amounts to about 10–20% compared with those produced by aggregated mycelium. It appears that the enzyme synthesis related to mycelium structure is independent of the mechanism which regulates the level of pectinase synthesis within a specific morphological structure.     

Cytochrome b of cob revertants in yeast. 1. Isolation and characterization of revertants derived from cob exon mutants of Saccharomyces cerevisiae

Summary About 300 revertants were derived from 44 cob ^- mutants, mapping in the structure coding regions (exon 1, 3, 4, 5, or 6) of the mitochondrial apocytochrome b gene in Saccharomyces cerevisiae, strain 777-3A. Most of the revertants could not be distinguished from the wild-type by means of physiological properties. Twenty-two revertants different in phenotype are described here in more detail.The suppressor mutations (sup ^a) that compensate the primary cob ^- mutations (i.e., restore growth on glycerol) are mitochondrially inherited. They were localized in the same cob exon regions as the respective primary mutations, except for one revertant with a primary mutation in exon 6 and a suppressor, 4.2 map units distant, which may be located either in intron 5 or downstream in exon 6.Of 21 suppressors 17 are closely coupled to the primary mutation with recombination frequencies of 0.1%–0.3%. An estimate predicts that in more than 80% of these revertants only one amino acid is altered at that point of the polypeptide corresponding to the cob ^- site in the gene.The most interesting revertant phenotypes are: (1) reduced growth rate on glycerol. The respective cob ^-/sup^a mutations are scattered over the whole cob region and cannot be correlated exclusively with special gene regions. (2) decreased cytochrome b content. The most extreme reductions (28% and 30% of wild-type level) were observed to be due to mutations located in the 5 proximal part of exon 1. The highest percentage of revertants with decreased cytochrome b content was predominantly found mapping in exon 3. Complications in protoporphyrin attachment or the chelatase reaction were assumed to be the basic lesion causing reduced cytochrome b content, since in 10 out of 11 revertants examined the polypeptide is produced at wild-type level. (3) shifted maximum absorption wavelength of cytochrome b. The double mutations of the respective revertants map in the middle part of exon 1, in exon 4 and exom 5. The corresponding regions in the polypeptide presumably surround the heme group.     

Tn916-induced mutations in the hemolysin determinant affecting virulence of Listeria monocytogenes.

A genetic determinant essential for hemolysin production by Listeria monocytogenes has been inactivated by insertion of transposon Tn916 into L. monocytogenes DNA. The transposon was transferred by means of conjugation of a streptomycin-resistant L. monocytogenes recipient strain with Streptococcus faecalis CG110 on membrane filters. Among the tetracycline-resistant transconjugants, mutants were detected which had lost hemolytic activity. When tested in a mouse model, these mutants appeared to have lost the virulence that characterizes the parental strain. An extracellular protein of 58,000 apparent molecular weight was eliminated in the nonhemolytic mutants. In some of the mutants, the decrease in the production of the 58,000-dalton protein was accompanied by the production of a new protein of 49,000 apparent molecular weight. Hemolytic revertants regained the hemolytic phenotype and virulence and produced the extracellular protein that characterizes the recipient strain. Hybridization studies with Tn916 DNA indicated that the transposon is present in EcoRI and HindIII fragments of the nonhemolytic mutants. Single copies of Tn916 were detected in the chromosomal DNA of two of the three nonhemolytic mutants that were studied in detail. In hemolytic, tetracycline-sensitive revertants Tn916 appeared to be completely excised from the chromosome.     

Accumulation of 6-Azauridine by Mutants of Brevibacterium ammoniagenes

From the inosine producing mutants of Brevibacterium ammoniagenes, KY 13761 was selected as a strain which produced 6-azauridine from 6-azauracil.

The conditions for the conversion were examined and the intermitent feeding of 6-azauracil was found effective for the accumulation.

In order to increase the accumulation, prototrophic revertants were induced from KY 13761 and KY 13021 was selected. By intermitent feeding of 6-azauracil of a final concentration of 6 mg per ml, a maximal accumulation, 12.4 mg/ml, of 6-azauridine was obtained with KY 13021.     

Insertion mutations in the control region of the Gal operon of E. coli. I. Biological characterization of the mutations

Summary Galactose negative mutations are described which reduce the maximum expression of all three gal genes about 100-fold. The residual enzyme synthesis is not or only slightly inducible.These pleiotropic mutations map in the control region of the gal operon. No recombination is observed between these mutations. All mutants revert spontaneously to a Gal⁺ phenotype. In some mutations wildtype-like as well as constitutive revertants are obtained. The frequency of reversion can be increased by nitrosoguanidine (NG) in all mutants. The revertants, induced by this mutagen, are of a constitutive type.     

Arginine and proline genes ofAspergillus niger

Summary Aspergillus niger mutants defective in arginine or proline biosynthesis have been isolated and 12 genetic loci were identified. Mutation was induced by low doses UV, and mutants were isolated after filtration enrichment. The mutants were classified according to their phenotype in growth tests and were further characterized in complementation tests. The arginine auxotrophic mutants represent nine complementation groups. Three additional complementation groups were found for mutants that could grow on proline (two of them on arginine too). Linkage group analysis was done in somatic diploids obtained from a mutant and a master strain with genetic markers on six chromosomes. Thearg genes belong to six different linkage groups and thepro genes to two. Onearg-mutant could be complemented by transformation with theA. nidulans arg B ⁺ gene, and thisA. niger gene thus appeared to be homologous to theA. nidulans arg B. We isolated anA. niger strain with theargB gene tightly linked with thenicA1 marker. This strain is very suitable as acceptor for transformation with anargB-plasmid, because transformants with inserts on the homologous site can be recognized and analyzed genetically using thenicA1 marker gene.