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Effect of glutamine on the induction of nitrate reductase (1995)

Li, Xiu-Zhen ; Larson, Dawn E. ; Glibetic, Marija ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 93 (1995), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Nitrate reductase (NR. EC 1.6.6.1/2) is a substrate inducible enzyme that could be repressed by its end product glutamine or amino acids. To test this hypothesis, 6-day-old maize seedlings (Zea mays cv. W64A × W182E) were grown hydroponically in a 1/10 strength Hougland's salt solution modified to contain no nitrogen. Previous experiments had established that after a 24-h induction with NO3− (5 mM KNO3−) the level of NR activity and protein had reached a constant level. In the present experiments when glutamine (5 mM) was included together with NO3−, there was a significant reduction in NR activity (34% of the control values). NR protein and NR mRNA accumulation in the root. In the shoot, on the other hand, glutamine additions had little or no effect on the levels of either NR activity (81% of control) or NR protein. Inhibition of glutamine synthetase by methionine sulfoximine (MSX) resulted in reduced levels of glutamine in both root and shoot tissues. Contrary in our prediction, however, it had no effect on NR activity and mRNA content in roots. In the shoot, on the other hand, there was a marked reduction of NR activity (34% of the control value) and NR protein, but no apparent effect on NR mRNA. When detached shoots were treated with MSX and other inhibitors of glutamine synthetase (tabtoxinine-β-lactam or phosphinothricin) the induction of NR activity by NO3− was also inhibited. Glutamine additions 15 or 50 mM to detached shoots had essentially no effect on the induction of NR activity (90% of control). These results demonstrate that the influence of glutamine and MSX on the induction of NR in maize root and shoot tissues, respectively, is very different.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb05125.x

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GA-binding protein is involved in altered expression of ribosomal protein L32 gene (1997)

Ćurčić, Dušica ; Glibetić, Marija ; Larson, Dawn E. ; [et al.]

New York, N.Y. : Wiley-Blackwell

Journal of Cellular Biochemistry 65 (1997), S. 287-307

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ISSN: 0730-2312

Keywords: GA-binding protein ; rpL32 gene promoter ; ribosomes ; differentiation/dedifferentiation ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Differentiation of BC3H1 myoblasts to myocytes is accompanied by a 67% drop in the rate of rpL32 gene transcription. Addition of high concentrations of serum to resting myocyte populations stimulates cell growth and subsequent dedifferentiation to proliferating myoblasts with a return to the normal rate of rpL32 gene transcription. During these growth rate changes the binding activities of previously identified factors (β, γ, δ) which interact with the rpL32 gene promoter were examined by mobility shift assays. Binding of the β factor (an Ets related protein) to an oligonucleotide containing the β element was reduced significantly in myocycle nuclear extracts, but subsequent dedifferentiation increased binding within 30 min in either the presence or absence of the cycloheximide. Binding of the γ and δ factors to their respective elements changed only slightly during these processes. Dephosphorylation of either myoblast or myocyte extracts resulted in increased binding of the β factor suggesting that binding activity of the β factor is modulated by phosphorylation during the changes in BC3H1 myoblasts growth rate. In addition, mobility shift assays with recombinant GABP α and β proteins and their specific antibodies revealed that GABP proteins bind to the rpL32 gene promoter in a sequence dependent manner, and that similar proteins are present in BC3H1 myoblast/myocyte extracts. These results support the premise that the GABP heterodimer is the rpL32 β factor. Furthermore, during BC3H1 myoblast differentiation and dedifferentiation neither the levels of the GABP α and β proteins nor their respective mRNAs change. These results suggest that GABP is a constitutively expressed protein and is involved in regulating rpL32 gene by post-transcriptional modifications. J. Cell. Biochem. 65:287-307. © 1997 Wiley-Liss, Inc.

Additional Material: 12 Ill.

Type of Medium: Electronic Resource

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