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71.
72.
Christopher R. Bailey Hugh A. Penfold Herbert N. Arst Jr. 《Molecular & general genetics : MGG》1979,169(1):79-83
Summary In Aspergillus nidulans expression of the gabA gene, the probable structural gene for the -amino-n-butyrate (GABA) permease, is controlled by induction, via the intA gene, ammonium repression, mediated by the areA gene, and probably carbon catabolite repression. Regulatory mutations, tightly linked to gabA, were selected by reverting an areA-2 strain on GABA as nitrogen source. These mutations, gabI-1, gabI-2, and gabI-3 result in increased gabA expression and are cis-dominant in their effects on the gabA gene. Mapping data show that the regulatory mutations map on one side of all gabA- alleles tested. 相似文献
73.
Total RNA was extracted from fast growing suspension cells of bean, the mRNA was translated and the products of protein synthesis analysed by gel electrophoresis. Actinomycin D (20 g ml–1) added to the cultures 12 h before the induction of phenylalanine ammonia-lyase (PAL) activity by naphthylacetic acid (NAA) (1 mg/l) and kinetin (0.2 mg/l) failed to prevent the increased activity of the enzyme usually produced by this ratio of the plant growth hormones. PAL was isolated and purified from suspension cultured bean cells. The purified enzyme ran as a single band on polyacrylamide gel electrophoresis. The protein translated from RNA prepared from induced and non-induced cells was separated by gel electrophoresis and the bands of protein on the gels were compared. There was no evidence for an increase in the amount of PAL synthesised in vitro from the mRNA of induced cells even though these had 5 times the amount of activity of the enzyme compared with that of the non-induced cells. The results indicate that the induction of PAL activity is not immediately preceeded by an increase in the synthesis of PAL-mRNA by the cells. The control of the activity of the enzyme is discussed with respect to this finding.Abbreviations PAL
phenylalanine ammonia-lyase
- NAA
3naphthylacetic acid
- DEAE
Diethylamino ethyl
- EDTA
Ethylenediamine tetraacetate
- SDS
Sodium dodecyl sulphate 相似文献
74.
75.
Detection of Mouse Mammary Tumor Virus RNA in BALB/c Tumor Cell Lines of Nonviral Etiologies 总被引:8,自引:5,他引:3
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Jaquelin P. Dudley Janet S. Butel Susan H. Socher Jeffrey M. Rosen 《Journal of virology》1978,28(3):743-752
A complementary DNA (cDNA) probe to mouse mammary tumor virus (MMTV) RNA was synthesized using calf thymus DNA oligonucleotides as a random primer. This probe was then used to study the expression of MMTV RNA in cell lines from BALB/c tumors induced in vivo either spontaneously or in response to viral, chemical, or hormonal stimuli. The cDNA had a length of approximately 400 to 500 nucleotides and specifically hybridized to MMTV RNA and BALB/c lactating mammary gland RNA, but not to Moloney leukemia virus RNA. Calf thymus DNA-primed cDNA could protect 50% of iodinated MMTV RNA from S1 nuclease digestion at cDNA-RNA ratios of 1:1 and 90% of labeled viral RNA at ratios of 10:1. Thermal denaturation of MMTV RNA-cDNA hybrids yielded a T(m) of 88.5 degrees C, indicative of a well-base-paired duplex. Screening of mouse mammary tumor cells for MMTV sequences revealed that three out of five lines of BALB/c origin had undetectable levels of viral RNA (相似文献
76.
Recombination inH-1, the major histocompatibility complex (MHC) of the rat, has defined two regions,H-1A andH-1B, which determine antigens apparently homologous to the KJD and Ia antigens of the mouse, respectively. Alloantisera directed at these antigens have been absorbed with kidney homogenates. The results showed that cells in the kidney express serologically detectable MHC antigens determined by both theH-1A andH-1B region. Control absorptions indicated that to account for these results in terms of recirculating lymphocytes, two perfused kidneys would need to contain more than 60 percent of the recirculating lymphocyte pool. It appears likely, therefore, that H-1B antigens are expressed by cells resident in the kidney. 相似文献
77.
Summary In an effort to establish the reasons for the limitations in the final ethanol concentration of Zymomonas mobilis fermentation, the effects of CO2 and ethanol on the fermentation were investigated using continuous and fed-batch cultivation systems. The nucleation and
stripping out of CO2 from the fermenter using diatomaceous earth or nitrogen gas or both exhibited a profound effect on the glucose uptake rate
during the early stages of fed-batch fermentation, but did not improve final ethanol yields. The addition of ethanol together
with above mentioned experiments confirmed conclusively that ethanol inhibition is responsible for the final ethanol concentration
obtainable during Zymomonas mobilis fermentation. The final concentration lies between 90 and 110 gl−1 or approximately 12–15% (v/v) ethanol. 相似文献
78.
Hugh B. Martin L.L. Houston 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1983,762(1):128-134
A conjugate containing α2-macroglobulin and highly purified ricin A chain was made using N-succinimidyl-3-(2-pyridyldithio)propionate. Radioimmunoassay indicated that it contained 1.2 mol A chain per mol α2-macroglobulin. The conjugate inhibited polyuridylic-acid directed translation by rat liver ribosomes and protein synthesis in human fibroblasts. There was a 90 min lag period before the beginning of inhibition in fibroblasts, but complete inhibition could be achieved. By measuring protein synthesis as a function of protein concentration, it was demonstrated that 8.25·10?9M conjugate was required to inhibit 50% of protein synthesis in 6 h. To achieve the same level of inhibition, 165-times more (1.3·10?6M) unconjugated A chain was required, and 180-times less ricin (4.6·10?11M). Ricin was more than 28 000 times more inhibitory than A chain alone. The presence of α2-macroglobulin did not increase the cytotoxicity of unconjugated A chain, and it even protected the cells to a slight extent. The inhibitory action of the conjugate was blocked by antibodies specific for α2-macroglobulin or ricin, and it was not prevented by galactose or antibodies specific for ricin B chain. Electron microscopy of the conjugate indirectly labelled with ferritin demonstrated that it was internalized by receptor mediated endocytosis through coated pits. These data indicate that the A chain portion of the conjugate survives the conditions in the lysosomes to the extent that it retains its ability to inactivate cytoplasmic ribosomes. 相似文献
79.
80.
Nancy L. Figler Dudley K. Strickland Margaretta Allietta Steven L. Gonias 《Journal of structural biology》1991,106(3)
α2-Macroglobulin (α2M) is a plasma proteinase inhibitor that binds up to 2 mole of proteinase per mole of inhibitor. Proteinase binding or reaction with small primary amines causes a major conformational change in α2M. As a result of this conformational change, a new epitope recognized by monoclonal antibody 7H11D6 is exposed. The association of α2M-proteinase or α2M-methylamine with α2M cellular receptors is prevented by 7H11D6. In this investigation, the binding of 7H11D6 to α2M was studied by electron microscopy. 7H11D6 bound to α2M-methylamine and α2M-trypsin but not to native α2M. The structure of α2M after conformational change resembled the letter “H.” 7H11D6 epitopes were identified near the apices of the four arms in the α2M “H” structure. 7H11D6 that was adducted to colloidal gold (7HAu) retained the specificity of the free antibody (binding to α2M-trypsin but not to native α2M). α2M conformational change intermediates prepared by sequential reaction with a protein crosslinker and trypsin also bound 7HAu. These results suggest that a complete α2M conformational change is not necessary for 7H11D6 epitope exposure and may not be required for receptor recognition. 7HAu was used to isolate a preparation consisting primarily of binary α2M-trypsin (1 mole trypsin per mole α2M instead of 2). Structures resembling the letter “H” were most common; however, each field showed some atypical molecules with arms that were compacted instead of thin and elongated. These incompletely transformed structures were similar to the α2M conformational intermediates described previously (S. L. Gonias and N. L. Figler (1989) J. Biol. Chem. 264, 9565–9570). We propose that lateral arm extension is a critical step in α2M conformational change. Failure of lateral arm extension is probably a common property of different α2M conformational intermediates. 相似文献