RESUMO
Yeast p20 is a small, acidic protein that binds eIF4E, the cap-binding protein. It has been proposed to affect mRNA translation and degradation, however p20's function as an eIF4E-binding protein (4E-BP) and its physiological significance has not been clearly established. In this paper we present data demonstrating that p20 is capable of binding directly to mRNA due to electrostatic interaction of a stretch of arginine and histidine residues in the protein with negatively charged phosphates in the mRNA backbone. This interaction contributes to formation of a ternary eIF4E/p20/capped mRNA complex that is more stable than complexes composed of capped mRNA bound to eIF4E in the absence of p20. eIF4E/p20 complex was found to have a more pronounced stimulatory effect on capped mRNA translation than purified eIF4E alone. Addition of peptides containing the eIF4E-binding domains present in p20 (motif âYTIDELF), in eIF4G (motif âYGPTFLL) or Eap1 (motif âYSMNELY) completely inhibited eIF4E-dependent capped mRNA translation (in vitro), but had a greatly reduced inhibitory effect when eIF4E/p20 complex was present. We propose that the eIF4E/p20/mRNA complex serves as a stable depository of mRNAs existing in a dynamic equilibrium with other complexes such as eIF4E/eIF4G (required for translation) and eIF4E/Eap1 (required for mRNA degradation).
Assuntos
Fator de Iniciação 4E em Eucariotos/química , Complexo Proteico Nuclear de Ligação ao Cap/química , RNA Mensageiro/química , Proteínas de Saccharomyces cerevisiae/química , Fatores de Complexo Ternário/química , Sequência de Aminoácidos/genética , Arginina/química , Sítios de Ligação , Fator de Iniciação 4E em Eucariotos/genética , Histidina/química , Complexo Proteico Nuclear de Ligação ao Cap/genética , Motivos de Nucleotídeos/genética , Ligação Proteica/genética , Estabilidade de RNA/genética , RNA Mensageiro/genética , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genética , Fatores de Complexo Ternário/genéticaRESUMO
Moringa oleifera is widely cultivated in plantations in the tropics and subtropics. Previous cultivation studies with M. oleifera focused primarily only on leaf yield. In the present study, the content of potentially health-promoting secondary metabolites (glucosinolates, phenolic acids, and flavonoids) were also investigated. Six different ecotypes were grown under similar environmental conditions to identify phenotypic differences that can be traced back to the genotype. The ecotypes TOT4880 (origin USA) and TOT7267 (origin India) were identified as having the best growth performance and highest secondary metabolite production, making them an ideal health-promoting food crop. Furthermore, optimal cultivation conditions-exemplarily on sulfur fertilization and water availability-for achieving high leaf and secondary metabolite yields were investigated for M. oleifera. In general, plant biomass and height decreased under water deficiency compared to normal cultivation conditions, whereas the glucosinolate content increased. The effects depended to a great extent on the ecotype.