Improved method for obtaining thymineless mutants of Escherichia coli and Salmonella typhimurium

Implementation of a loss-of-function system to determine growth and stress-associated mutagenesis in Bacillus subtilis

A forward mutagenesis system based on the acquisition of mutations that inactivate the thymidylate synthase gene (TMS) and confer a trimethoprim resistant (Tmpr) phenotype was developed and utilized to study transcription-mediated mutagenesis (TMM). In addition to thyA, Bacillus subtilis possesses thyB, whose expression occurs under conditions of cell stress; therefore, we generated a thyB- thyA+ mutant strain. Tmpr colonies of this strain were produced with a spontaneous mutation frequency of ~1.4 × 10-9. Genetic disruption of the canonical mismatch (MMR) and guanine oxidized (GO) repair pathways increased the Tmpr frequency of mutation by ~2-3 orders of magnitude. A wide spectrum of base substitutions as well as insertion and deletions in the ORF of thyA were found to confer a Tmpr phenotype. Stationary-phase-associated mutagenesis (SPM) assays revealed that colonies with a Tmpr phenotype, accumulated over a period of ten days with a frequency of ~ 60 ×10-7. The Tmpr system was further modified to study TMM by constructing a ΔthyA ΔthyB strain carrying an IPTG-inducible Pspac-thyA cassette. In conditions of transcriptional induction of thyA, the generation of Tmpr colonies increased ~3-fold compared to conditions of transcriptional repression. Further, the Mfd and GreA factors were necessary for the generation of Tmpr colonies in the presence of IPTG in B. subtilis. Because GreA and Mfd facilitate transcription-coupled repair, our results suggest that TMM is a mechanim to produce genetic diversity in highly transcribed regions in growth-limited B. subtilis cells.

An alternative pathway for reduced folate biosynthesis in bacteria and halophilic archaea

Whereas tetrahydrofolate is an essential cofactor in all bacteria, the gene that encodes the enzyme dihydrofolate reductase (DHFR) could not be identified in many of the bacteria whose genomes have been entirely sequenced. In this communication we show that the halophilic archaea Halobacterium salinarum and Haloarcula marismortui contain genes coding for proteins with an N-terminal domain homologous to dihydrofolate synthase (FolC) and a C-terminal domain homologous to dihydropteroate synthase (FolP). These genes are able to complement a Haloferax volcanii mutant that lacks DHFR. We also show that the Helicobacter pylori dihydropteroate synthase can complement an Escherichia coli mutant that lacks DHFR. Activity resides in an N-terminal segment that is homologous to the polypeptide linker that connects the dihydrofolate synthase and dihydropteroate synthase domains in the haloarchaeal enzymes. The purified recombinant H. pylori dihydropteroate synthase was found to be a flavoprotein.

Development of a chromosome-plasmid balanced lethal system for Lactobacillus acidophilus with thyA gene as selective marker

A chromosome-plasmid balanced lethal gene delivery system for Lactobacillus acidophilus based on the thyA gene was developed. The selected L. acidophilus DOM La strain carries a mutated thyA gene and has an obligate requirement for thymidine. This strain can be used as a host for the constructed shuttle vector pFXL03, lacking antibiotic-resistant markers but having the wild-type thyA gene from L. casei which complements the thyA chromosomal mutation. The vector also contains the replicon region from plasmid pUC19 and that of the Lactococcus plasmid pWV01, which allows the transfer between Escherichia coli, L. casei and L. acidophilus. Eight unique restriction sites (i.e., PstI, HindIII, SphI, SalI, AccI, XbaI, KpnI and SacI) are available for cloning. After 40-time transfers in modified MRS medium, no plasmid loss was observed. The vector pFXL03 is potentially useful as a food-grade vaccine delivery system for L. acidophilus.

Thymine metabolism and thymineless death in prokaryotes and eukaryotes

For many years it has been known that thymine auxotrophic microorganisms undergo cell death in response to thymine starvation [thymineless death (TLD)]. This effect is unusual in that deprivation of many other nutritional requirements has a biostatic, but not lethal, effect. Studies of numerous microbes have indicated that thymine starvation has both direct and indirect effects. The direct effects involve both single- and double-strand DNA breaks. The former may be repaired effectively, but the latter lead to cell death. DNA damaged by thymine starvation is a substrate for DNA repair processes, in particular recombinational repair. Mutations in recBCD recombinational repair genes increase sensitivity to thymineless death, whereas mutations in RecF repair protein genes enhance the recovery process. This suggests that the RecF repair pathway may be critical to cell death, perhaps because it increases the occurrence of double-strand DNA breaks with unique DNA configurations at lesion sites. Indirect effects in bacteria include elimination of plasmids, loss of transforming ability, filamentation, changes in the pool sizes of various nucleotides and nucleosides and in their excretion, and phage induction. Yeast cells show effects similar to those of bacteria upon thymine starvation, although there are some unique features. The mode of action of certain anticancer drugs and antibiotics is based on the interruption of thymidylate metabolism and provides a major impetus for further studies on TLD. There are similarities between TLD of bacteria and death of eukaryotic cells. Also, bacteria have "survival" genes other than thy (thymidylate synthetase), and this raises the question of whether there is a relationship between the two. A model is presented for a molecular basis of TLD.

PHYSIOLOGICAL STATE OF ESCHERICHIA COLI AND THE INHIBITION OF DEOXYRIBONUCLEIC ACID SYNTHESIS BY PHENETHYL ALCOHOL

Treick, R. W. (Indiana University, Bloomington), and W. A. Konetzka. Physiological state of Escherichia coli and the inhibition of deoxyribonucleic acid synthesis by phenethyl alcohol. J. Bacteriol. 88:1580-1584. 1964.-The effects of concentration of phenethyl alcohol (PEA) and the physiological state of the cells on inhibition of macromolecular synthesis in Escherichia coli were investigated. Deoxyribonucleic acid (DNA) synthesis by cells of E. coli from the maximum stationary phase is completely inhibited by 0.32% (v/v) PEA immediately upon addition of the inhibitor, although there is a net increase in the synthesis of ribonucleic acid (RNA) and protein. However, DNA synthesis in cells from the exponential phase is inhibited only after an increase which corresponds to 1.4 to 1.6 times the amount of DNA present at the time of PEA addition. In a randomly dividing culture, this increment of DNA synthesis presumably represents completion of the DNA replication cycle initiated at the time of PEA addition. By programming the addition and removal of PEA, DNA synthesis can be made to proceed in stepwise increments corresponding to doublings of the DNA. The data indicate that the DNA being replicated at the time of PEA addition completes the replication cycle and, although there is net synthesis of RNA and protein, no initiation of a second cycle of DNA replication occurs until the removal of the inhibitor.

THYMINELESS MUTATION SITE ON ESCHERICHIA COLI CHROMOSOME

Kitsuji, Nobuo (Kanazawa University, Kanazawa, Ishikawa, Japan). Thymineless mutation site on Escherichia coli chromosome. J. Bacteriol. 87:802-808. 1964.-Kinetic studies of the recombinant formation in crosses between Escherichia coli K-12 Hfr H, Hfr C, or Hfr P10 as donor and F(-)W1177thy(-)his(-) as recipients showed that the time of appearance of thy(+)Sm(r) recombinants lay between that of xyl(+)Sm(r) and his(+)Sm(r), indicating that the thy gene lies between the xyl and his markers. Genetic analysis of recombinants of the Hfr C x W117thy(-)his(-) cross further indicated that the thy gene is located on the chromosome between the Sm marker and the his marker. In matings between seven independently isolated thymineless mutants of Hfr P10 and F(-)W1177thy(-)his(-), thy(+) recombinants of various recombination rates appeared. Thus, it was suggested that in E. coli K-12 the thy gene occupies some region between the Sm marker and the his marker on the chromosome, and that there are many thymineless mutation sites in it.

CHROMOSOMAL LOCATION OF THYMINE AND ARGININE GENES IN ESCHERICHIA COLI AND AN F' INCORPORATING THEM

Ishibashi, Masahide (Osaka University, Osaka, Japan), Yoshinobu Sugino, and Yukinori Hirota. Chromosomal location of thymine and arginine genes in Escherichia coli and an F' incorporating them. J. Bacteriol. 87:554-561. 1964.-The gene responsible for thymine requirement or independence in Escherichia coli K-12 is located on the chromosome, near Arg(2) (arginine) and between Sm (streptomycin) and Ade (adenine). A new F' (called F(15)) carrying the Thy (thymine) gene as well as the Arg(2) gene was discovered. The Thy(+) (thymine independent) gene on F(15) relieves the defect of all Thy(-) (thymine requiring) mutants of E. coli examined, such as E. coli 15 T(-), B3, and Thy(-) mutants obtained by aminopterine treatment. It can also be transferred to Thy(-) mutants of Salmonella typhimurium and Serratia marcescens, converting them to Thy(+).

Thymidylate synthase gene from Lactococcus lactis as a genetic marker: an alternative to antibiotic resistance genes

The potential of the thymidylate synthase thyA gene cloned from Lactococcus lactis subsp. lactis as a possible alternative selectable marker gene to antibiotic resistance markers has been examined. The thyA mutation is a recessive lethal one; thyA mutants cannot survive in environments containing low amounts of thymidine or thymine (such as Luria-Bertani medium) unless complemented by the thyA gene. The cloned thyA gene was strongly expressed in L. lactis subsp. lactis, Escherichia coli, Rhizobium meliloti, and a fluorescent Pseudomonas strain. In addition, when fused to a promoterless enteric lac operon, the thyA gene drove expression of the lac genes in a number of gram-negative bacteria. In transformation experiments with thyA mutants of E. coli and conjugation experiments with thyA mutants of R. meliloti, the lactococcal thyA gene permitted selection of transformants and transconjugants with the same efficiency as did genes for resistance to ampicillin, chloramphenicol, or tetracycline. Starting from the broad-host-range plasmid pGD500, a plasmid, designated pPR602, was constructed which is completely free of antibiotic resistance genes and has the lactococcal thyA gene fused to a promoterless lac operon. This plasmid will permit growth of thyA mutant strains in the absence of thymidine or thymine and has a number of unique restriction sites which can be used for cloning.

Septicemia caused by cysteine-dependent Escherichia coli

A case of septicemia and urinary tract infection caused by cysteine-dependent Escherichia coli in a 70-year-old woman with bilateral staghorn calculi is described. This is the second report of a cysteine-dependent E. coli bacteremia. The bacterium was falsely susceptible to ampicillin and co-trimoxazole when tested on a medium without cysteine supplement.

Characterization of an ATP-dependent DNA strand transferase from human cells

We have characterized an enzymatic activity from human cell nuclei which is capable of catalyzing strand exchange between homologous DNA sequences. The strand exchange activity was Mg2+ dependent and required ATP hydrolysis. In addition, it was capable of promoting reannealing of homologous DNA sequences and could form nucleoprotein networks in a fashion reminiscent of purified bacterial RecA protein. Using an in vitro recombination assay, we also showed that the strand exchange activity was biologically important. The factor(s) responsible for the activity has been partially purified.

Characterization of an ATP-dependent DNA strand transferase from human cells

We have characterized an enzymatic activity from human cell nuclei which is capable of catalyzing strand exchange between homologous DNA sequences. The strand exchange activity was Mg2+ dependent and required ATP hydrolysis. In addition, it was capable of promoting reannealing of homologous DNA sequences and could form nucleoprotein networks in a fashion reminiscent of purified bacterial RecA protein. Using an in vitro recombination assay, we also showed that the strand exchange activity was biologically important. The factor(s) responsible for the activity has been partially purified.

Toxicity of the pyrimidine biosynthetic pathway intermediate carbamyl aspartate in Salmonella typhimurium

Growth of Salmonella typhimurium pyrC or pyrD auxotrophs was severely inhibited in media that caused derepressed pyr gene expression. No such inhibition was observed with derepressed pyrA and pyrB auxotrophs. Growth inhibition was not due to the depletion of essential pyrimidine biosynthetic pathway intermediates or substrates. This result and the pattern of inhibition indicated that the accumulation of the pyrimidine biosynthetic pathway intermediate carbamyl aspartate was toxic. This intermediate is synthesized by the sequential action of the first two enzymes of the pathway encoded by pyrA and pyrB and is a substrate for the pyrC gene product. It should accumulate to high levels in pyrC or pyrD mutants when expression of the pyrA and pyrB genes is elevated. The introduction of either a pyrA or pyrB mutation into a pyrC strain eliminated the observed growth inhibition. Additionally, a direct correlation was shown between the severity of growth inhibition of a pyrC auxotroph and the levels of the enzymes that synthesize carbamyl aspartate. The mechanism of carbamyl aspartate toxicity was not identified, but many potential sites of growth inhibition were excluded. Carbamyl aspartate toxicity was shown to be useful as a phenotypic trait for classifying pyrimidine auxotrophs and may also be useful for positive selection of pyrA or pyrB mutants. Finally, we discuss ways of overcoming growth inhibition of pyrC and pyrD mutants under derepressing conditions.

Physiological and enzymatic properties of a thymidine-requiring Pediococcus cerevisiae mutant

We describe the isolation and characterization of a Pediococcus cerevisiae thymidine-requiring mutant and its thymidine-independent revertant. The mutant strain lacked thymidylate synthetase activity and had an absolute requirement for low concentrations (2 micrograms/ml) of thymidine in addition to a requirement for N-5-formyl tetrahydrofolic acid (folinate). Even at high concentrations (up to 500 micrograms/ml), thymine could not replace thymidine. In contrast to its wild-type parent, which grows only on folinate, the thymidine-requiring mutant (Thy- Fol+) was able to take up and grow on picogram quantities of unreduced folic acid. When both strains were grown on folinate, the Thy- Fol+ strain was at least 10(3)-fold more resistant to the folic acid analogs aminopterin and methotrexate than the wild-type strain. On the other hand, when grown on folic acid, the Thy- Fol+ strain was as sensitive to the folic acid analogs as the Thy+ Fol+ strain and was 10(2)-fold more sensitive than the wild-type strain grown on folinate. The thymidine-independent revertant (Thy+ Fol+) regained the wild-type level of thymidylate synthetase activity, but maintained the ability to take up and grow on unreduced folic acid like its Thy- Fol+ parent.

Thymidine uptake and utilization in Escherichia coli: a new gene controlling nucleoside transport

A commonly used strain of Escherichia coli K-12 was shown to be deficient in the transport of a number of nucleosides, including thymidine. Thymidine incorporation was unaffected. Strain AB2497 exhibited a strikingly lower thymidine pulse-label incorporation at low (less than 1 mug/ml) thymidine concentrations than do many other strains. The deficiency appeared to be due to mutation in a single gene. This gene, which we designated nup (for nucleoside uptake), is located at 10 to 13 min on the E. coli linkage map. In nup+ strains, the transport of a given nucleoside was relatively insensitive to large excesses of other nucleosides but was competitively inhibited by the same nucleoside. Mutants deficient inthymidine kinase are deficient in thymidine uptake but normal in deoxyadenosine uptake. A two-step model for nucleoside transport is presented in which the first step, utilizing the nup gene product, is a nonspecific translocation of nucleoside to the interior of the cell. In the second step, the individual nucleosides are modified by cellular enzymes (e.g., nucleosides kinases) facilitate accumulation.

Thymine-requiring bacteria associated with co-trimoxazole therapy

Since 1971 thymine-requiring (thy-) pathogens have been isolated from the urine of 8 patients with renal calculi, and from the sputum of 1 patient with chronic chest infection. The patients had been treated with co-trimoxazole for several months before the isolation of the mutant pathogens. There was persistent pyuria in the patients with renal calculi, and purulent sputum in the patient with chronic chest infection. The mutants were identified by their inability to grow on diagnostic sensitivity test agar (D.S.T., Oxoid) which is deficient in thymine. It was found that wild-type bacteria can produce growth factors for the metabolism of the mutants in vitro, and the urine of the patients contained by thymine-like compounds. These findings indicate that thy- mutants may develop in renal calculi during co-trimoxazole therapy. Therapy should be changed to a more suitable antimicrobial as soon as possible after diagnosis of mutant infection.

Interference of dna ts mutations of Escherichia coli with thymineless death

Thermosensitive mutants of Escherichia coli in which deoxyribonucleic acid replication is inhibited at high temperature have been assayed for their response to thymine deprivation at permissive and nonpermissive temperatures. The survival rate of mutants in which initiation of replication is defective at 42 C (dnaA and dnaC-D) is much higher at nonpermissive temperatures than at 32 C. By contrast, thymineless death is not hindered at 42 C in two elongation mutants (dnaE and dnaG). Bacterial strains belonging to the dnaB class exhibit both types of behavior. These results are in accordance with the model linking thymineless death to a disruption of an active replication fork. We discuss the possibility that the dnaB protein takes part in this process of cell decay.

Isolation of an Escherichia coli mutant deficient in glutathione synthesis

A mutant of Escherichia coli that contains essentially no detectable glutathione has been isolated. The mutant contains a very low level of the enzyme glutathione synthetase and accumulates lambda-glutamyl cysteine at a concentration approximately equal to the level of glutathione found in its parent. No significant differences in growth were observed between the mutant and its parent. However, the activity of at least one enzyme was found to be affected by the absence of glutathione; the specific activity of the B1 subunit of ribonucleoside diphosphate reductase was greatly reduced. The possibility that the decreased B1 activity is due to a mutation in the structural gene coding for B1 or its regulatory gene could be eliminated. This suggests that one role of glutathione in the cell is to maintain at least this one protein in an active state. We propose the designation gshB for the gene coding for glutathione synthetase.

Mutations affecting glutamine synthetase activity in Salmonella typhimurium

A positive selection procedure has been devised for isolating mutant strains of Salmonella typhimurium with altered glutamine synthetase activity. Mutants are derived from a histidine auxotroph by selecting for ability to grow on D-histidine as the sole histidine source. We hypothesize that the phenotype may be based on a regulatory increase in the activities of the D-histidine racemizing enzymes, but this has not been established. Spontaneous glutamine-requiring mutants isolated by the above selection procedure have two types of alterations in glutamine synthetase activity. Some have less than 10% of parent activity. Others have significant glutamine synthetase activity, but the enzyme have an altered response to divalent cations. Activity in mutants of the second type mimics that of highly adenylylated wild-type enzyme, which is believed to be in-active in vivo. Glutamine synthetase from one such mutant is more heat labile than wild-type enzyme, indicating that it is structurally altered. Mutations in all strains are probably in the glutamine synthetase structural gene (glnA). They are closely linked on the Salmonella chromosome and lie at about min 125. The mutants have normal glutamate dehydrogenase activity.

Obligate thymidine auxotrophs of Pseudomonas acidovorans

The aminopterin technique was adapted for the isolation of thymidine auxotrophs of Pseudomonas acidovorans. All the mutants isolated responded to thymidine but not to thymine.

Development of bacteriophage alpha. II. Dependence on the host ribonucleic acid polymerase

Measurements of ribonucleic acid (RNA) synthesis using (14)C-uracil uptake in rifampin-sensitive and rifampin-resistant strains of Bacillus megatherium were carried out after infection of the bacteria with bacteriophage alpha. Phage development was inhibited in the former but not the latter strain, showing that alpha phage development is dependent on the bacterial host RNA polymerase. This dependence exists at all times during eclipse. RNA polymerase extracts showed the same in vitro rifampin sensitivity as the corresponding bacterial strains.

Effect of the folic acid analogue, trimethoprim, on growth, macromolecular synthesis, and incorporation of exogenous thymine in Escherichia coli

The effect of trimethoprim [2,4-diamino-5(2',4',5'trimethoxybenzyl)-pyrimidine] in the presence of thymine on Escherichia coli B temperature-sensitive and non-temperature-sensitive Thy(') strains and a phosphodeoxyribomutase-negative mutant was studied. The inhibitory effect of 5 mug of trimethoprim per ml on the growth of E. coli B was not overcome by thymine, thymidine, or thymidylate even in the presence of one-carbon metabolites and related metabolites. Deoxyribonucleic acid (DNA) and protein synthesis were more severely inhibited than ribonucleic acid (RNA) synthesis. The inhibition of DNA synthesis was partially reversed by addition of deoxyadenosine to increase the incorporation of exogenous thymine. By contrast, the inhibition of protein was not reversed even with one-carbon metabolites present, in keeping with the requirement for formylmethionyl-transfer RNA(F) for initiation. However, the inhibition of both DNA and protein synthesis in a phosphodeoxyribomutase-negative strain by 1 mug of trimethoprim per ml with thymine present was partially reversed by deoxyadenosine and one-carbon metabolites, and nearly normal growth occurred. 5-Fluorodeoxyuridine added at the time of addition of trimethoprim prevented the inhibition. Sulfadiazine in the presence of thymine inhibited both Thy(+) and Thy(-) strains whereas trimethoprim (with thymine) did not inhibit Thy(-) organisms. The effect of trimethoprim on the incorporation of labeled thymine into DNA was also studied. These experiments support the concept that trimethoprim in conjunction with the action of thymidylate synthetase inhibits the growth of Thy(+) cells because of a depletion of tetrahydrofolate. DNA synthesis is inhibited initially by a limitation of thymine nucleotide precursor, resulting from the indirect inhibition of thymidylate synthetase and the poor incorporation of exogenous thymine.

Genetic regulation of ribonucleoside and deoxyribonucleoside catabolism in Salmonella typhimurium

Four enzymes involved in ribonucleoside and deoxyribonucleoside catabolism (deoxyribose-5-P aldolase, thymidine phosphorylase, phosphodeoxyribomutase, and purine nucleoside phosphorylase) are coded for by four closely linked structural genes on the Salmonella chromosome. The genetic order of these genes is (deoC-deoA-deoB-deoD)-serB-thr. Studies on polarity mutants and induction patterns indicate that the deoB and deoD genes may constitute a single operon and that the deoC and deoA genes may constitute a second closely linked operon.

Kinetics of adsorption of colicin CA42-E2 and reversal of its bactericidal activity

The kinetics of killing of Escherichia coli K-12 by colicin CA42-E2 have been studied, and the data were used to estimate the adsorption constant of this colicin under various environmental conditions. Evidence was obtained suggesting that the adsorption of colicin occurred in two stages; the earlier stage was reversible and did not lead to the death of the cell, the latter stage was irreversible and bactericidal. Cells which had adsorbed a lethal quantity of colicin could be rescued for a short time by inactivating the adsorbed colicin with trypsin. However, when the metabolic activity of the cells was totally arrested the lethal effect of adsorbed colicin was subject to trypsin reversal over long periods of time.

2-Deoxyribose gene-enzyme complex in Salmonella typhimurium: regulation of phosphodeoxyribomutase

Phosphodeoxyribomutase, the enzyme which catalyzes the interconversion of 2-deoxyribose-1-phosphate to 2-deoxyribose-5-phosphate, has been partially purified from Salmonella typhimurium. The enzyme had an absolute requirement for manganese ion and was stimulated by glucose-1, 6-diphosphate. Phosphodeoxyribomutase was induced by deoxyribose-5-phosphate and was coordinately regulated with the enzymes thymidine phosphorylase and deoxyribose-5-phosphate aldolase, type II. Mutants deficient in these three enzymes were isolated and mapped close to the threonine locus in S. typhimurium. The three enzymes thymidine phosphorylase, deoxyribose-5-phosphate aldolase, type II, and phosphodeoxyribomutase are controlled by a series of linked genes and appear to constitute an operon.

Nutrition of Myxococcus xanthus FBa and some of its auxotrophic mutants

A defined medium containing 15 amino acids plus salts was used to study the nutrition of Myxococcus xanthus FBa. The amino acids phenylalanine, leucine, isoleucine, valine, and methionine were essential for growth, whereas glycine, proline, asparagine, alanine, lysine, and threonine stimulated growth. An unusual pattern of requirement was found in the aromatic amino acids. Phenylalanine was essential and served as the precursor of tyrosine. Growth in the absence of tryptophan was adaptive, with cells reaching a growth rate equal to that of controls after a lag of about a week. (14)C-labeled ribose and glucose were not appreciably metabolized. Auxotrophs requiring purines and pyrimidines were isolated and were used to study the fate of externally supplied nucleic acid derivatives. Appropriate mutants could satisfy their requirements with free bases, nucleosides, and nucleotides, and could hydrolyze nucleic acids and use the products. However, studies using (14)C-ribose-labeled uridine (isolated from a Salmonella typhimurium pyrimidine auxotroph) showed that externally supplied nucleic acid derivatives were incorporated almost solely into the nucleic acids of the myxobacters, with little used either for energy-yielding oxidations or other cell anabolism.

Mutants of Escherichia coli defective in ribonucleoside and deoxyribonucleoside catabolism

From Escherichia coli B, mutants were prepared that lacked the enzymes adenosine deaminase, cytidine deaminase, and purine nucleoside phosphorylase. In each case, the mutant lacked enzyme activity for both ribonucleoside and deoxyribonucleoside. Mutants lacking purine nucleoside phosphorylase lost the capacity to cleave the nucleosides of adenine, guanine, and hypoxanthine.

2-deoxyribose gene-enzyme complex in Salmonella typhimurium. I. Isolation and enzymatic characterization of 2-deoxyribose-negative mutants

Salmonella typhimurium was found to utilize 2-deoxyribose as a sole carbon and energy source. Cells grown in the presence of deoxyribose contained increased levels of deoxyribose kinase, thymidine phosphorylase, and two forms of deoxyribose-5-phosphate aldolase (DR5P aldolase). One form of DR5P aldolase was induced by deoxyribose and coordinately regulated with deoxyribose kinase. The second form of DR5P aldolase was induced by deoxyribose-5-phosphate and coordinately regulated with thymidine phosphorylase. Mutants unable to ferment deoxyribose have been isolated and shown to be lacking either deoxyribose kinase or deoxyribose permease, but none has been found from which DR5P aldolase is missing. Thymine-requiring mutants which are able to grow on low levels of thymine have been isolated and shown, in some cases, to be lacking one or both DR5P aldolases.