Biochemical characterization and messenger specificity of polypeptide chain initiation factors from Escherichia coli

Three protein factors are required for maximum poly(U, G)- or AUG-directed binding of fMet-tRNA to ribosomes. The same three factors are both necessary and sufficient for “natural” mRNA-directed binding of fMet-tRNA to ribosomes. Bound fMet-tRNA cosediments with the 70S ribosome as does bound mRNA. All three factors are required for the fMet-tRNA and GTP-dependent binding of mRNA to the 70S initiation complex.     

Hormonal Regulation of Source-sink Relationship: Effect of Hormones on Excised Source and Sink Organs of Cereals

The regulatory role of plant growth substances in relation tosource and sink activity was studied. Leaching of electrolytesfrom flag leaf cells increased with age. Abscisic acid, however,increased the permeability of leaf cells at 10^–4 M andlower concentrations. Plant growth regulators like auxin, gibberellinand cytokinin at 10^–5 M inhibited the leaching of electrolytesbut slightly enhanced the process at 10^–3 M. The effluxof ¹⁴C-sucrose loaded on the flag leaves was not detectablein the very early stage of panicle development but was prominentin the later stages. While auxin prevented sucrose efflux atall stages of panicle development, gibberellin and cytokininwere effective only in different degrees. All the three growthregulators enhanced the activity of -amylase in the flag leafcells but protease activity was enhanced only by gibberellin.Synthesis of polymers like starch, DNA, RNA and protein in developingrice grains was stimulated by gibberellin, cytokinin and auxinlargely in the order mentioned. (Received September 2, 1986; Accepted May 22, 1987)     

Ultrastructural morphology of ectoplacental cone trophoblasts of hamster embryos.

The invasiveness of trophoblast cells is well known, but it is not clear whether they achieve this property by being transformed to other cell types (like malignant ones) or remain benign. Trophoblasts, in culture, were studied ultrastructurally by examining the surface morphology of the cell vis-à-vis their cytoplasmic outgrowth, and the presence and/or absence of ruffling membranes, filopodia, microvilli, pinocytotic pits or bleb-like structures was observed. Results revealed formation of ruffling membranes only on the leading edge, a presence of slender filopodia and pinocytotic pits but an absence of microvilli and bleb-like structures, the characteristic features of a transformed cell. The study indicated that the trophoblast cells, in spite of being invasive, do not convert to any other cell type.     

The relationship between heat-stress and photobleaching in green and blue-green algae

Two characteristic temperatures were identified from measurements of the temperature dependence of O₂ evolution by Chlorella vulgaris and Anacystis nidulans: T₁, the threshold temperature for inhibition of O₂ evolution under saturating light conditions, and T₂, the upper temperature limit for O₂ evolution. Measurement of delayed light emission from photosystem II (PSII) showed that it passed through a maximum at T₁ and was virtually eliminated on heating the samples to T₂. Related changes were observed in low-temperature (77K) fluoresence emission spectra. Heat-stress had little effect on the absorption properties of the cells at temperatures below T₁ but incubation at higher temperatures, particularly under high-light conditions, resulted in extensive absorption losses. An analysis of these measurements suggests that this increased susceptibility to photobleaching is triggered by an inhibition of the flow of reducing equivalents from PSII that normally serves to protect the light-harvesting apparatus of the cells from photo-oxidation. Adaptation to higher growth temperatures resulted in increases in the values of T₁ and T₂ for Anacystis nidulans but not for Chlorella vulgaris.Abbreviations PSI photosystem I - PSII photosystem II - Chl a chlorophyll a - Chl b chlorophyll b - DCMU 3-(3 4 dichlorophenyl)-11-dimethylurea - PC plastocyanin - APC allophycocyanin CIW-DPB Publication No. 887.     

Cloning and characterization of the p42 subunit of mammalian translation initiation factor 3 (eIF3): demonstration that eIF3 interacts with eIF5 in mammalian cells.

Eukaryotic translation initiation factor 3 (eIF3) is a large multisubunit protein complex that plays an essential role in the binding of the initiator methionyl-tRNA and mRNA to the 40S ribosomal subunit to form the 40S initiation complex. cDNAs encoding all the subunits of mammalian eIF3 except the p42 subunit have been cloned in several laboratories. Here we report the cloning and characterization of a human cDNA encoding the p42 subunit of mammalian eIF3. The open reading frame of the cDNA, which encodes a protein of 320 amino acids (calculated Mr35 614) has been expressed in Escherichia coli and the recombinant protein has been purified to homogeneity. The purified protein binds RNA in agreement with the presence of a putative RNA binding motif in the deduced amino acid sequence. The protein shows 33% identity and 53% similarity with the Tif35p subunit (YDR 429C) of yeast eIF3. Transfection experiments demonstrated that polyhistidine-tagged p42 protein, transiently expressed in human U20S cells, was incorporated into endogenous eIF3. Furthermore, eIF3 isolated from transfected cell lysates contains bound eIF5 indicating that a specific physical interaction between eIF5 and eIF3 may play an important role in the function of eIF5 during translation initiation in eukaryotic cells.     

A unique example of a pseudo-peptide containing noncoded amino acids self-assembling into a supramolecular β-sheet-like structure in crystals

The crystal structure of a pseudo-peptide with noncoded amino acids (such as N-substituted 3-aminophenylacetic acid and -aminoisobutyric acid) exhibits almost an extended backbone conformation and this pseudo-peptide self-assembled to form an infinite hydrogen bonded, supramolecular, antiparallel -sheet-like structure in solid state.