Effect of streptomycin on the stoichiometry of GTP hydrolysis in a poly(U)-dependent cell-free translation system

The technique of Sepharose-bound template translation has been used to estimate the stoichiometry of GTP hydrolysis during peptide elongation in the presence of streptomycin. The presence of streptomycin has been shown to have no great effect on the elongation rate and the stoichiometry of GTP hydrolysis during codon-specific peptide elongation in the poly(U)-directed translation system: the molar ratio of hydrolysed GTP to incorporated phenylalanine was about 2. At the same time streptomycin exerted a significant effect during misreading when a ribosome-bound peptide in the poly(U)-programmed system was elongated by leucine or isoleucine residues: the miselongation was stimulated and hence the ratio of hydrolysed GTP per peptide bond was strongly reduced, as compared with the excessive GTP hydrolysis which is characteristic of the misreading system in the absence of streptomycin [(1984) FEBS Lett. 178, 283-287]. The conclusion has been made that streptomycin blocks the stage of correction ('proof-reading') following GTP hydrolysis during EF-Tu-dependent aminoacyl-tRNA binding.     

Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

A surplus no more? Variation in krill availability impacts reproductive rates of Antarctic baleen whales

The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human-induced changes. Understanding how climate-mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8-year dataset (2013–2020), we show that inter-annual humpback whale pregnancy rates, as determined from skin-blubber biopsy samples (n = 616), are positively correlated with krill availability and fluctuations in ice cover in the previous year. Pregnancy rates showed significant inter-annual variability, between 29% and 86%. Our results indicate that krill availability is in fact limiting and affecting reproductive rates, in contrast to the krill surplus hypothesis. This suggests that this population of humpback whales may be at a threshold for population growth due to prey limitations. As a result, continued warming and increased fishing along the WAP, which continue to reduce krill stocks, will likely impact this humpback whale population and other krill predators in the region. Humpback whales are sentinel species of ecosystem health, and changes in pregnancy rates can provide quantifiable signals of the impact of environmental change at the population level. Our findings must be considered paramount in developing new and more restrictive conservation and management plans for the Antarctic marine ecosystem and minimizing the negative impacts of human activities in the region.     

Study of localization of the protein-synthesizing machinery along actin filament bundles.

Indirect immunofluorescent microscopy was used to study the distribution of elongation factor 2 (eEF-2) in fixed human skin diploid and mouse embryo fibroblasts. It was found earlier that some of the eEF-2 ribosomes and initiation factor 2 (eIF-2) are co-localized with a part of the actin microfilament bundles in these cells (Gavrilova et al., 1987; Shestakova et al., 1991). Here it has been shown that inhibition of protein synthesis either by inactivation of eEF-2 itself with diphtheria toxin or by inactivation of ribosomes with ricin does not abolish the distribution of eEF-2 along the actin microfilament bundles. At the same time, the disassembly of actin microfilaments by cytochalasin D results also in the disappearance of eEF-2-carrying threads. This means that the eEF-2-carrying threads do not exist per se, and that the organization of eEF-2 in visible "filaments" depends upon the integrity of the actin cytoskeleton.     

Factor-free and one-factor-promoted poly(U,C)-dependent synthesis of polypeptides in cell-free systems from Escherichia coli

α-Tropomyosin from rat cardiac muscle was shown by two-dimensional gel electrophoresis to become phosphorylated when tissue slices were incubated in Eagle's medium supplemented with ³²P_i. In the adult rat and mouse heart the level of phosphorylation was ～30%, but the level was much higher in the foetal heart (60–70%). A similar developmental trend was observed in skeletal muscle from the rat and mouse, where phosphorylated forms of both α- and β-tropomyosins were observed. When rat cardiac cells were grown in tissue culture in the presence of ³²P_i, radioactivity was incorporated into the region of the gel containing tropomyosin.     

Citrulline metabolism in normal and citrullinemic human lymphocyte lines

Citrullinemia is one of the five aminoacidurias associated with the Krebs-Henseleit urea cycle. A long-term lymphocyte line (UM-21) derived from a patient with this disease and nine of ten clones of this line were found to have no activity for the enzyme argininosuccinate synthetase (AS), as demonstrated by their inability to grow in medium in which citrulline had been substituted for arginine, by their inability to incorporate arginine-C14 derived from citrulline-C14 into cellular protein, and by direct enzyme assay. One clone had normal or nearly normal argininosuccinate synthetase activity, as demonstrated by the same criteria. Nutritional "variants" able to grow logarithmically in medium containing citrulline were isolated from UM-21 and three clones. The apparent Kms of AS for citrulline in UM-21, the ten clones, the variant lines, and a normal line were measured and fell into three groups: AS in UM-21 and nine clones had no measurable apparent Km for citrulline; AS in the variant cells had apparent Kms for citrulline of approximately 20 mM; and AS in the normal cell line and one clone had apparent Kms for citrulline of 0.2 mM. The data suggest that the defect in the citrullinemic cell lines is due to a mutation in the structural gene coding for argininosuccinate synthetase.     

Isolation and immunochemical study of monomer and dimer forms of IgA human globulins]

Monomer and dimer of myeloma IgA human globulins are isolated by means of electrophoresis, ionic exchange chromatography, gel filtration and immunoadsorbtion. They are shown to be homogenous (using analytical ultracentrifugation and immunochemical analysis) and to differ in their antigenic specificity. Dimeric form of IgA has additional antigenic determinants, which depend on the intactness of a polymer structure and which are destroyed after protein dissociation into subunits in the presence of beta-mercaptoethanol. Reconstructed polymers are polydispersed subunit aggregates, they do not have polymeric determinants inherent to native polymers.