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1.
Kinetics of degradation of labelled proteins was followed in two asporogenic mutants ofBacillus megaterium during incubation in a sporulation medium. Both the mutant producing exocellular protease (KM 1prn
+) and the mutant not producing the enzyme (KM 12prn) were found to contain a labile protein fraction, whose proportion decreases with prolonged time of labelling and whose half-life
is about 1 h. Most proteins were relatively stable and were degraded at a rate of 1 %/h and 2 %/h in strains KM 1 and KM 12,
respectively (half life 70–80 h and 35–40 h in strains KM 1 and KM 12, respectively). The intracellular proteolytic activity
of the KM 12 mutant remains practically the same during incubation in the sporulation medium or slowly increases. The labile
protein fraction practically disappears from the cells after a 3.5-h incubation. When such a culture is then subjected to
a shift-up and transferred again to the sporulation medium, the rate of protein turnover temporarily increases. The temporary
increase of the turnover rate is caused by a partial replenishment of the labile protein fraction rather than by an accelerated
degradation of the relatively stable fraction. The intracellular proteolytic activity does not increase under these conditions.
The wild sporogenic strain ofB. megaterium also contains the labile protein fraction. Its half protein life is 1 h or less. However, the second protein fraction is
degraded much more rapidly than in the asporogenic mutants and its half life is 6–7 h. 相似文献
2.
Niels P. Fiil Berthe M. Willumsen J. D. Friesen Kaspar von Meyenburg 《Molecular & general genetics : MGG》1977,150(1):87-101
Summary Mutants in thespoT gene have been isolated as stringent second site revertants of therelC mutation. These show varying degrees of the characteristics associated with thespoT1 gene,viz relative amount and absolute levels of both pppGpp and ppGpp and the decay rate of the latter. The entry of3H-guanosine into GTP and ppGpp pools inspoT
+ andspoT1 cells either growing exponentially or during amino acid starvation was determined, and the rate of ppGpp synthesis and its
decay constant calculated. During exponential growth the ppGpp pool is 2-fold higher, its decay constant 10-fold lower, and
its synthesis rate 5-fold lower inspoT
- than inspoT
+ cells; during amino acid starvation the ppGpp pool is 2-fold higher, its decay constant 20-fold lower, and its synthesis
rate 10-fold lower inspoT than inspoT
+ cells. In one of the “intermediate”spoT mutants the rate of entry of3H-guanosine into GTP, ppGpp and pppGpp was measured during amino acid starvation. The data form the basis of a model for the
interconversion of the guanosine nucleotides in which the flow is:GDP→GTP→pppGpp→ppGpp→Y. Calculations of the rates of synthesis and conversion of pppGpp and ppGpp under various conditions in variousspoT
+ andspoT
- strains indicate that the ppGpp concentration indirectly controls the rate of pppGpp synthesis.
ThespoT1 allele was introduced into various relaxed mutants. It was shown that many phenomena associated with the relaxed response
ofrelC and “intermediate”relA mutants were phenotypically suppressed when thespoT1 allele was introduced into these mutants. These double mutants exhibit ppGpp accumulation, rate of RNA accumulation, rate
of β-galactosidase synthesis, and heat lability of β-galactosidase synthesized during amino acid starvation similar to the
stringent wild-type. It is concluded that the relaxed response is due directly to the lack of ppGpp and that the stringest
response is due directly to ppGpp. 相似文献
3.
Intracellular proteolytic activity increased during incubation of the sporogenic strain ofBacillus megaterium KM in a sporulation medium together with excretion of an extracellular metalloprotease. The exocellular protease activity
in a constant volume of the medium reached a 100-fold value with respeot to the intracellular activity. Maximal values of
the activity of both the extracellular and intracellular enzyme were reached after 3 – 5 h of incubation. After 7 h 20 – 50%
cells formed refractile spores. The intracellular proteolytic system hydrolyzed denatured proteinsin vitro at a rate up to 150 μg mg-1 h-1 and native proteins at a rate up to 70 μg mg-1 h-1. Degradation of proteinsin vivo proceeded from the beginning of transfer to the sporulation medium at a constant rate of 40 μg mg-1 h-1 and the inactivation of beta-galactosidase at a rate of 70 μg mg-1 h-1. The intracellular proteolytic activity was inhibited to 65 – 88% by EDTA, to 23 – 76% by PMSF. Proteolysis of denatured
proteins was inhibited both by EDTA and PMSF more pronouncedly than proteolysis of native proteins; 50 – 65% of the activity
were localized in protoplasts.
Another strain ofBacillus megaterium (J) characterized by a high (up to 90%) and synchronous sporulation activity was found to behave in a similar way, but the
rate of protein turnover in this strain was almost twice as high. The asporogenic strain ofBacillus megaterium KM synthesized the exocellular protease in the sporulation medium, but its protein turnover was found to decrease substantially
after 3 – 4 h. The intraeellular proteolytic system of the sporogenic strain J and the asporogenic strain KM were also inhibited
by EDTA and PMSF. 相似文献
4.
The effect of nitrate deprivation on cell growth and nucleotide level was studied in Anacystis nidulans. A 10-fold reduction in nitrate level resulted in a drastic slowdown of growth. Upon addition of nitrate to the starving cultures, after a lag period, the cells resumed growth.Nutritional shift-down induced a transitory expansion of the guanosine tetraphosphate (ppGpp) pool, preceeded by a transitory increase in GTP and ATP concentrations. After having reached peak values, the concentration of ppGpp, GTP and ATP dropped to the respective base levels. The expansion of the ppGpp pool was found to be due to an increase in ppGpp synthesis, rather than to a decrease in ppGpp breakdown. After nutritional shift-up, no decrease in the ppGpp level was found.In starving cells, a decrease in free amino acids was observed to occur concomitantly with the expansion of the ppGpp pool. The level of free amino acids started to increase simultaneously with the contraction of the ppGpp pool. 相似文献
5.
A temperature increase from 35° to 40–42°C enhances the rise of cytoplasmic serine proteinase (ISP1) activity in Bacillus megaterium incubated in a sporulation medium. A temperature shift from 27°C in the growth medium to 35°C in the sporulation medium has the same effect. Elevated temperature stimulates the increase of ISP1 level when applied immediately after the transfer of cells from the growth to the sporulation medium (at T0) or at T3, when sporulation becomes irreversible. The cytoplasmic PMSF-resistant activity or the proteolytic activity associated with the membrane fraction is stimulated only slightly or not at all. A temperature increase to 45–47°C suppresses the rise of proteolytic activities in all cell fractions. In addition to the elevation of the ISP1 activity by an upward temperature shift, the rise of this enzyme in nongrowing cells is also stimulated by osmotic stress. In growing populations, in contrast to the rise of the ISP1 activity caused by elevated temperature in nongrowing cells, this proteinase is induced by low temperatures (24–27°C). The ISP1 activity roughly correlates with the enzyme protein concentration determined by immunoblotting. 相似文献
6.
The temperature permissive for sporulation (up to 42°C) inBacillus megaterium is by 4–5°C lower than that for its growth (up to 46–47°C). The ability ofB. megaterium cells to synthesize and degrade stress proteins under incubation in the sporulation medium was therefore investigated. The
higher level of hsp 70, a typical stress protein induced by a temperature shock in postexponential growth phase, did not increase
the permissive temperature of sporulation. The hsp 70 protein did not undergo a rapid turnover and its portion in the soluble
protein fraction did not drop for at least 6 h at a temperature that was nonpermissive for sporulation (43.5°C). On the other
hand, the elevated level of hsp 70 could not bring about the inhibition of sporulation as it was retained in the cells even
after a shift of the temperature to 35°C, permitting sporulation of the culture. 相似文献
7.
T. P. Pirog T. A. Shevchuk Yu. A. Klimenko 《Applied Biochemistry and Microbiology》2010,46(6):599-606
Activity of key enzymes of n-alkane metabolism was determined in cells of Rhodococcus erythropolis EK-1, a surfactant producer grown on n-hexadecane. Potassium cations were found to inhibit alkane hydroxylase and NADP+-dependent aldehyde dehydrogenase, while sodium cations were found to activate these enzymes. Decreased potassium concentration
(to 1 mM), increased sodium concentration (to 35 mM), and addition of 36 μmol/l Fe(II), required for alkane hydroxylase activity,
resulted in increased activity of the enzymes of n-hexadecane metabolism and in a fourfold increase of surfactant synthesis. A 1.5–1.7-fold increase in surfactant concentration
after addition of 0.2% fumarate (gluconeogenesis precursor) and 0.1% citrate (lipid synthesis regulator) to the medium with
n-hexadecane results from enhanced synthesis of trehalose mycolates, as evidenced by a 3–5-fold increase in phosphoenolpyruvate
synthetase and trehalose phosphate synthase, respectively. 相似文献
8.
Evidence that Bacillus subtilis sporulation induced by the stringent response is caused by the decrease in GTP or GDP. 总被引:9,自引:6,他引:3
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Partial amino acid deprivation of Bacillus subtilis, which evokes the stringent response, initiates sporulation not because the highly phosphorylated guanine nucleotides guanosine-5'-diphosphate-3'-diphosphate (ppGpp) and guanosine-5'-triphosphate-3'-diphosphate (pppGpp) increase but because GTP decreases. This was shown with a mutant (Myc) partially resistant to mycophenolate, an inhibitor of IMP dehydrogenase. Upon amino acid deprivation, the Myc mutant (62032) showed the usual increase in ppGpp and pppGpp but a reduced decrease in GTP, and only few cells sporulated. Extensive sporulation was restored by the addition of mycophenolate or decoyinine, and inhibitor of GMP synthetase, which caused a further decrease in GTP. 相似文献
9.
Response of Guanosine 5′-Triphosphate Concentration to Nutritional Changes and Its Significance for Bacillus subtilis Sporulation 总被引:4,自引:4,他引:0
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We have investigated the changes in the guanosine 5'-triphosphate (GTP) and P-ribosyl-PP pools in stringent and relaxed strains of Bacillus subtilis under conditions frequently used to initiate sporulation. After a shift-down from a Casamino Acids-glutamate to a glutamate medium (Sterlini-Mandelstam shift-down), the pools of adenosine 5'-triphosphate and P-ribosyl-PP increased in both strains; in the stringent strain, ppGpp and pppGpp increased and GTP decreased rapidly, whereas in the relaxed strain, ppGpp and pppGpp increased only slightly and GTP decreased only slowly and less extensively. The stringent strain sporulated well, whereas the relaxed strain sporulated late and poorly. Addition of decoyinine, an inhibitor of guanosine 5'-monophosphate synthetase, caused a further decrease of GTP and initiated good sporulation of the relaxed strain. After a shift-down from a glucose-lactate to a lactate medium (Ramaley-Burden shift-down) the pool of P-ribosyl-PP (and GTP) decreased in both strains, indicating a shortage of purine precursors. This shift-down also caused a stringent response which prevented the consumption of nucleotides, as shown by the maintenance of adenosine 5'-triphosphate at a high concentration in the stringent strain but not in the relaxed strain. After a delay, the relaxed strain, in which GTP decreased as fast as in the stringent strain, sporulated also as efficiently. In nutrient sporulation medium the stringent strain and, less effectively, the relaxed strain accumulated ppGpp and pppGpp transiently towards the end of exponential growth. Eventually, the P-ribosyl-PP pool decreased drastically in both strains. In all cases the initiation of sporulation was correlated with a significant decrease of GTP. Granaticin, an antibiotic which prevents the charging of leucyl-transfer ribonucleic acid, was used to show that the stringent response inhibited the formation of xanthosine monophosphate from inosine monophosphate. It prevented the accumulation of xanthosine monophosphate in decoyinine-treated cultures of the stringent strain but not in those of the relaxed strain. 相似文献
10.
A translational lacZ fusion of the Bacillus subtilis mscL gene that encodes the mechanosensitive channel of large conductance (MscL) was expressed at significant levels during log phase growth of B. subtilis, and the level of mscL–lacZ expression was increased 1.5-fold by growth in medium with high salt (1 M NaCl). However, in growth media with either low or high salt, mscL–lacZ expression fell drastically beginning in the late log phase of growth, and fell to even lower levels during sporulation, although a significant amount of β-galactosidase from mscL to lacZ was accumulated in the developing spore. Deletion of mscL had no effect on B. subtilis growth, sporulation or subsequent spore germination. The ΔmscL strain also grew as well as the wild-type parental strain in medium with 1.2 M NaCl. While log phase wild-type cells grown with 1.2 M NaCl survived a rapid 0.9 M osmotic downshift, log phase ΔmscL cells rapidly lost viability and lysed when subjected to this same osmotic downshift. However, by the early stationary phase of growth, ΔmscL cells had become resistant to a 0.9 M osmotic downshift. 相似文献
11.
Koizumi S Yonetani Y Maruyama A Teshiba S 《Applied microbiology and biotechnology》2000,53(6):674-679
Improved strains for the production of riboflavin (vitamin B2) were constructed through metabolic engineering using recombinant DNA techniques in Corynebacterium ammoniagenes. A C. ammoniagenes strain harboring a plasmid containing its riboflavin biosynthetic genes accumulated 17-fold as much riboflavin as the host
strain. In order to increase the expression of the biosynthetic genes, we isolated DNA fragments that had promoter activities
in C. ammoniagenes. When the DNA fragment (P54-6) showing the strongest promoter activity in minimum medium was introduced into the upstream
region of the riboflavin biosynthetic genes, the accumulation of riboflavin was 3-fold elevated. In that strain, the activity
of guanosine 5′-triphosphate (GTP) cyclohydrolase II, the first enzyme in riboflavin biosynthesis, was 2.4-fold elevated whereas
that of riboflavin synthase, the last enzyme in the biosynthesis, was 44.1-fold elevated. Changing the sequence containing
the putative ribosome-binding sequence of 3,4-dihydroxy-2-butanone 4-phosphate synthase/GTP cyclohydrolase II gene led to
higher GTP cyclohydrolase II activity and strong enhancement of riboflavin production. Throughout the strain improvement,
the activity of GTP cyclohydrolase II correlated with the productivity of riboflavin. In the highest producer strain, riboflavin
was produced at the level of 15.3 g l−1 for 72 h in a 5-l jar fermentor without any end product inhibition.
Received: 23 August 1999 / Received revision: 13 October 1999 / Accepted: 5 November 1999 相似文献
12.
The clastogenic effect ofN-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster ovary (CHO) cells and its modulation by Na2SeO3 and caffeine were studied by metaphase analysis of chromosome aberrations (CA) as well as by measuring the formation and
repair of single-strand (ss) DNA breaks employing hydroxylapatite chromatography. Treatment of CHO cells with MNNG (1.25 or
2.5 × 10-5M) for 3 h caused CA in 11 and 19% of metaphases scored, respectively. Pretreatment of cells with Na2SeO3 (1–5 μg/mL) or caffeine (0.2–2.0 mg/mL) for 2 h resulted in a 2–3.5-fold increase of CA frequency. Addition of both modulators
during the mutagen exposure tended to cause a slight inhibition of clastogenic activity of MNNG (1.25 × 10−5
M) or had no effect on CA number when MNNG was used at a concentration of 2.5 × 10−5M. Posttreatment of CHO cells with Na2SeO3 for 20 h after MNNG was ineffective in influencing the number of metaphases with CA, whereas, at these conditions, caffeine
enhanced up to 6-7-fold the clastogenic activity of MNNG. Addition of both modulators during the whole experiment, 2 h pretreatment
included, resulted in a further significant increase of CA frequency up to the total pulverization of chromosomes in all metaphases
scored. The coclastogenic effect of caffeine was greater in this case. The enhancement of chromosome-damaging activity of
MNNG by selenite and caffeine was better expressed when this carcinogen was applied at the higher concentration used. An additive
coclastogenic effect was observed in CHO cells treated simultaneously with Na2SeO3 and caffeine plus MNNG. In addition, the treatment of CHO cells with MNNG (5 × 10−6
M) caused a rapid increase of ssDNA breaks number reaching maximal values after 30–45 min. However, up to 50–60% of MNNG-induced
ssDNA breaks were repaired during the first 60–150 min after the mutagen exposure. The 2 h pretreatment of CHO cells with
Na2SeO3 (2 μg/mL) or the addition of this trace element after MNNG had no effect on formation and repair of MNNG-induced ssDNA breaks.
The coclastogenic effect of Na2SeO3 in CHO cells treated with MNNG was not directly linked to the induction and disappearance of ssDNA breaks measured by hydroxylapatite
chromatography. 相似文献
13.
The effect of the organic buffer salts MES, MOPS, and PIPES on the growth of S. thermophilus ST110, medium pH, and accumulation of the antipediococcal bacteriocin thermophilin 110 were evaluated in whey permeate media
over a period of 24 h. In nonbuffered medium, thermophilin 110 production at 37°C paralleled the growth of S. thermophilus ST110 and reached a maximum after 8–10 h. Addition of organic buffer salts decreased the drop in medium pH and resulted in
increased biomass (dry cells; μg/mL) and higher yields of thermophilin 110 (units/μg cells). The best results were obtained
by the addition of 1% (w/v) MES to the medium, which reduced the pH drop to 1.8 units after 10 h of growth (compared to 2.3
pH units in the control) and resulted in a 1.5-fold increase in cell mass (495 μg/mL) and a 7-fold increase in thermophilin
110 yield (77 units/μg dry cells) over the control. The results showed that whey permeate-based media may be suitable for
producing large amounts of thermophilin 110 needed for controlling spoilage pediococci in industrial wine and beer fermentations.
Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 相似文献
14.
Inhibition caused by rapid changes in the environment has earlier been observed in hybridoma cultures following deliberate
step-changes in the culture environment. This paper presents evidence of similar effects occurring during the normal span
of continuous cultures fed enriched medium at low dilution rates (0.002–0.005 1/h). The effect of this observation on optimisation
is discussed. In continuous culture at a dilution rate of 0.013 1/h, a viable cell density of 4×109 cells/l was achieved by gradually increasing the nutrient concentration in the feed medium. The MAb titre was 200 mg/l representing
a 6-fold increase compared to batch culture and a 2-fold increase compared to continuous culture using standard medium. 相似文献
15.
Payot S Guedon E Desvaux M Gelhaye E Petitdemange E 《Applied microbiology and biotechnology》1999,52(5):670-674
The nutritional and physiological factors affecting sporulation of Clostridium cellulolyticum were studied using steady-state continuous cultures grown in both complex and synthetic media. Under cellobiose limitation,
the probability that cells will sporulate appears to be directly related to the growth rate. In complex medium, the highest
percentage of sporulation was 20% at a dilution rate of 0.015 h−1 whereas in synthetic medium it was 10% at 0.035 h−1. In both media, when the dilution rate was either higher or lower the percentage of sporulation decreased by between 2% and
4%. At low dilution rates, endospore formation was repressed under cellobiose-sufficient concentrations, suggesting catabolite
repression by cellobiose. Furthermore, the concentration of ammonium was important in determining the percentage of sporulation,
as ammonium limitation induced extensive sporulation at low growth rates even in an excess of cellobiose. The sporulation
process is not triggered when cells are cellobiose-exhausted both in complex and synthetic media. These data suggest that,
in C. cellulolyticum, an exogenous supply of carbon is required throughout the sporulation process. In the experimental conditions used in this
work, no relationship between glycogen accumulation or glycogen mobilization and endospore formation was detected in C. cellulolyticum.
Received: 15 April 1999 / Received revision: 15 June 1999 / Accepted: 22 June 1999 相似文献
16.
InBacillus megaterium, a temperature that suppresses sporulation (43°C) only slightly exceeds both the optimum growth temperature and the temperature
still permitting sporulation (40–41°C). Here we show that, when cells grown at 35°C and transferred to a sporulation medium,
were subjected to shifts between 35°C and the sporulation suppressing temperature (SST, 43°C), their development and proteolytic
activities were deeply affected. During the reversible sporulation phase that took place at 35°C for 2–3 h (T2–T3), the cells developed forespores and their protein turnover was characterized by degradation of short-lived proteins and
proteins made accessible to the proteolytic attack because of starvation. During the following irreversible sporulation phase
refractile heat-resistant spores appeared at T4–T5. Protein turnover rate increased again after T2 and up to T8 60–70% prelabelled proteins were degraded. The SST suppressed sporulation at its beginning; at T3 no asymmetric septa were observed and the amount of heat-resistant spores at T8 was by 4–5 orders lower than at 35°C. However, the cells remained viable and were able to sporulate when transferred to a
lower temperature. Protein degradation was increased up to T3 but then its velocity sharply dropped and the amount of degraded protein at T8 corresponded to slightly more than one-half of that found at 35°C. The cytoplasmic proteolytic activity was enhanced but
the activity in the membrane fraction was decreased. When a temperature shift to SST was applied at the beginning of the irreversible
sporulation phase (T2.5), the sporulation process was impaired. A portion of forespores lyzed, the others were able to complete their development
but most spores were not heat-resistant and their coats showed defects. Protein degradation increased again because an effective
proteolytic system was developed during the reversible sporulation phase but the amount of degraded protein was slightly lower
than at 35°C. A later (T4) shift to SST had no effect on the sporulation process. 相似文献
17.
Increased ethanol concentration in the nutrient medium gradually slowed down the growth ofEscherichia coli cells. However, during growth in the presence of 5% ethanol, DNA synthesis per cell increased about 2.5-fold compared to
control cells. There was a 40–45% increase in plasmid copy number in the ethanol-treated cells. 相似文献
18.
M. O. Emel’yanov Yu. A. Kim A. F. Korystova L. N. Kublik V. V. Shaposhnikova Yu. N. Korystov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(2):212-219
The effect of a short-time (1 h) oxidative stress on multidrug resistance (MDR) of murine leukemic P388VR cells has been investigated.
We studied the production of reactive oxygen species (ROS) in cells depending on the composition of medium and the concentration
of cells and hydrogen peroxide, as well as the effect of hydrogen peroxide on MDR of cells. MDR was determined from the transport
of calcein acetoxymethyl ester out of the cells and from a change in cell sensitivity to vincristine. The amount of ROS arising
in cells was determined using 2′,7′-dichlorodihydrofluorescein diacetate (DCFH2-DA). It was shown that the rate of ROS formation in cells decreases after the addition of serum to the medium and with an
increase of the cell number. By the action of hydrogen peroxide, the amount of ROS increases directly with its concentration.
Oxidative stress generated by 30–300 μM hydrogen peroxide decreases the MDR of the cells. The effect of hydrogen peroxide
increases with the treatment duration and concentration of hydrogen peroxide. MDR determined by the criterion of the efflux
of calcein ester from cells is completely suppressed after 1-h exposure to 300 μM hydrogen peroxide. At a concentration of
hydrogen peroxide of 60 μM and treatment duration of 1 h, the sensitivity of P388VR cells to vincristine increases to reach
the sensitivity of the wild-type P388 cells. Rapid (about 1 h) suppression of MDR is caused by inhibition of the activity
of transport proteins. MDR decrease induced by oxidative stress can be used in therapy of tumors resistant to anticancer drugs. 相似文献
19.
Yongqiang Ma Rong Zhang Guangyu Sun Haixia Zhu Ming Tang Jean C. Batzer Mark L. Gleason 《Mycological Progress》2010,9(2):151-155
Zygophiala qianensis is described as a new fungal species associated with the cuticle of apple fruit sampled from an orchard in Shaanxi Province,
China. Conidiophores were separate, arising from superficial hyphae, erect, scattered, subcylindrical, irregularly flexuous,
consisting of four parts: a hyaline supporting cell that gives rise to a smooth, dark brown stipe, terminating in a finely
verruculose, medium brown apical cell that gives rise to (1–)2(–3) medium brown, finely verruculose, doliiform to ellipsoidal,
polyblastic conidiogenous cells, with 1–2 prominent scars, apical and lateral, darkened, thickened. Conidia were solitary,
fusiform to obclavate, hyaline, smooth and thick-walled, transversely (0–)1(–7)-septate, mostly 1–2-septate, prominently constricted
at the septum; apex obtuse, base subtruncate, with a darkened, thickened hilum. Zygophiala qianensis is compared morphologically to other species of Zygophiala, and a phylogenetic analysis of their DNA sequence data is presented. 相似文献
20.
Initiation of Bacillus subtilis sporulation by the stringent response to partial amino acid deprivation 总被引:20,自引:0,他引:20
We have controlled the rates at which three different amino acids were available to auxotrophs of Bacillus subtilis by avoiding active transport of the respective substrate. The active transport of oxomethylvalerate, a precursor of isoleucine, was prevented by a kauA mutation, the uptake of L-aspartate was competed by 20 mM L-glutamate, and D-methionine was used instead of L-methionine. When in this way conditions of partial amino acid deprivation were achieved, a partial "stringent response" occurred which included the increase of ppGpp and pppGpp, and the decrease of GTP; such conditions initiated sporulation. In the corresponding relaxed (relA) mutants, the changes of guanine nucleotides were greatly reduced and no sporulation was observed at any substrate concentration; but addition of decoyinine produced a further decrease of GTP and caused sporulation. 相似文献