Reversible inactivation of tRNA nucleotidyltransferase from baker's yeast by tRNAPhe containing iodoacetamide-alkylated 2-thiocytidine in normal and additional positions.

2-Thiocytidine 5'-triphosphate, s2CTP, is able to replace CTP as a substrate for tRNA nucleotidyltransferase. s2CMP can be incorporated into both cytidine sites of the C-C-A terminus common to all tRNAs, and in the absence of ATP into at least two additional positions. This was shown by alkylation of the 2-thiocytidine residues with iodo[14C]acetamide, total nucleoside analysis, microgel electrophoresis and analysis of RNase T1 fragments of these tRNAs. The incorporation of the 3'-terminal AMP is not influenced by the additional s2CMP residues at pH 9.0. However, at pH 7.6 the additional s2CMP residues are hydrolysed and AMP can be incorporated into the normal position. Two different tRNAs with terminal 2-thiocytidine alkylated by iodoacetamide inhibit tRNA nucleotidyltransferase. This inhibition is significantly slower if an elongated species is used compared to a tRNA with alkylated 2-thiocytidine in the normal position 75. The addition of 2-mercaptoethanol reactivates the enzyme and leads to a cytidine containing tRNA. This reaction identifies the attacking nucleophile of the enzyme as cysteine residue, which is probably identical to a cysteine residue found in a similar experiment reported previously. The mechanism of the enzymatic and chemical reactions is discussed.     

Expression of the H-Y Antigen on thymus cells and skin: Differential genetic control linked toK end ofH-2

The strength of the H-Y antigen on thymus cells and on skin was compared in differentH-2-congenic mouse strains using a host-versus-graft reaction popliteal lymph node assay, and skin grafts from males of parental strains grafted to F₁ hybrid females. The results revealed considerable differences in the strength of the H-Y antigen among different congenic strains; these differences demonstrate the effect of theH-2-linked gene on the expression of the H-Y antigen. The linkage withH-2 was also confirmed in tests with segregating F₂ generations. In the strains bearing recombinantH-2 haplotypes, the strength of the H-Y antigen is similar to that of parental strain from which the recombinant received itsK end, and the responsible gene (or genes) map to the left ofI-C. The effect of theH-2-linked gene(s) on thymus cells and skin is different. The gene linked to theK end ofH- 2^b determines a strong H-Y antigen on thymus cells, but a relatively weak H-Y antigen on skin. The gene linked to theK end ofH- 2^k determines a weak H-Y antigen on thymus cells, but a strong H-Y antigen on skin. The gene linked to theK end ofH- 2^d determines a weak H-Y antigen on both thymus cells and skin. Our observations raise the possibility that the structural gene for the H-Y antigen is linked toH-2. Alternative (but not exclusive) explanations invoke regulatory effects ofH-2 on the expression of the H-Y antigen, possibly by means of the control of the cellular andogen receptors.     

Studies on mode of action of a bacteriocin from Clostridium septicum.

A bacteriocin was found in the supernatant fluid of Clostridium septicum strain Ovinus. Sensitivity to the bacteriocin was confined to other strains of C. septicum and to strains of C. chauvoei; the other Gram-positive and Gram-negative bacteria tested for sensitivity were unaffected by the bacteriocin. The bacteriocin killed sensitive cells rapidly but cell lysis did not appear to be involved. The bacteriocin inhibited protein and RNA synthesis immediately after its addition to sensitive cells; DNA synthesis was inhibited 10 min later.     

Microbial oxidation of elemental sulphur in brown soil

Plant and Soil - Brown soil formed from loamy clay was examined for its ability to produce sulphate from added elemental suphur. At higher rates of sulphur applications the pH of a slightly acid...     

Ca2+ ions, an allosteric activator of calcium uptake in rat liver mitochondria

In a previous investigation, I have shown that the kinetics of the Ca uniporter change fundamentally when mitochondria have transitorily lost their membrane potential. The sigmoidal kinetics, usually observed in liver mitochondria, became almost hyperbolic. This means an increase in the affinity for calcium, and hence a considerable acceleration of Ca uptake in the range of low, e.g., physiological calcium concentration. In this investigation I show that extramitochondrial calcium released from the deenergized mitochondria causes the allosteric activation of the Ca uniporter. The dependence of the allosterical activation on the extramitochondrial Ca2+ concentration and on time is described. It is also reported that it is possible to activate allosterically the Ca uniporter of energized mitochondria by a short-term elevation of the extramitochondrial Ca2+ concentration. The process of activation is reversible. It is quickly reversed by the addition of chelators for Ca2+, and it is slowly reversed when the activating Ca2+ has to be removed by the mitochondrial Ca uniporter, though the bulk of extramitochondrial calcium is taken up by it very quickly. Several kinetics of the Ca uniporter are described. The implications of continually changing kinetics of the Ca uniporter are considered for carbon tetrachloride intoxication and the action of alpha 1-adrenergic agonists in liver cells.     

An Efficient and Reliable Method of DNA Extraction from Meyna spinosa — A Traditional Medicinal Plant from North-East India

A simple, efficient and reliable CTAB method is standardized for genomic DNA isolation from fresh young leaves of a traditional medicinal plant Meyna spinosa. Key steps in the modified procedure include additional chloroform: isoamyl alcohol (24:1, v/v) extraction, addition of 4% PVP in the extraction buffer and an overnight isopropanol precipitation at room temperature. This procedure yields a high amount (46 μg DNA g^?1 fresh leaf tissue) of good quality DNA free from contaminants. The isolated DNA is suitable for digestion with EcoRI and HindIII restriction enzymes and can be used in other DNA manipulation techniques.     

Characterizing the socially transmitted foraging tactic “sponging” by bottlenose dolphins (Tursiops sp.) in the western gulf of Shark Bay,Western Australia

Individual foraging tactics are widespread in animals and have ecological and evolutionary implications. Indo‐Pacific bottlenose dolphins (Tursiops sp.) in Shark Bay, Western Australia, exhibit a foraging tactic involving tool use, called “sponging.” Sponging is vertically, socially transmitted through the matriline and, to date, has been described in detail in the eastern gulf of Shark Bay (ESB). Here, we characterize sponging in the western gulf of Shark Bay (WSB), in which a different matriline engages in the behavior. We identified 40 individual “spongers” in 9 mo of boat‐based surveys over three field seasons. As is the case in ESB, the majority of WSB spongers was female and engaged in sponging in deep channel habitats. In contrast to ESB, however, there was no difference in the number of associates between spongers and nonspongers in WSB, and activity budgets differed between spongers and deep‐water nonspongers; spongers foraged more frequently and rested less than nonspongers. Group sizes in deep channel habitat, where sponging was prevalent, were typically larger than those in shallow habitat, except for foraging, perhaps indicative of higher predator abundance and/or scattered prey distribution in deep‐water habitat. This research improves our understanding of within‐population foraging variations in bottlenose dolphins.