Increased myocardial pyrimidine nucleotide synthesis in isoproterenol-induced cardiac hypertrophy in rats

In a first phase (up to 12^h) after the first injection of isoproterenol (5mg.kg^?1 b.w.) the pyrimidine nucleotide pools were increased and the rates of incorporation of inorganic phosphate into the α-phosphate groups of nucleotides were raised from 16 to 58 nmol.g^?1.h^?1 for uracil nucleotides and from 11 to 32 nmol.g^?1.h^?1 for cytosine nucleotides. At a later stage, while the pool sizes decreased slowly toward control levels, these rates of labelling also decreased though still remaining above control values. A similar pattern of changes was induced by the eighth daily isoproterenol injection, but the alterations were attenuated.     

Identification of RNA molecules which contain 5 S ribosomal RNA and transfer RNA in an RNAase E-RNAase P- double mutant strain of Escherichia coli

In the analysis of DNAase II digestion of chromatin, as described in the preceding paper, interactions between adjacent nucleosomes play an important part. In order to understand the mechanism of DNAase II cleavage we next investigated the role of histone H1 in these interactions and characterized the nucleoprotein particles arising in the course of DNAase II action.H1-free chromatin prepared by three different procedures, using either 0.6 m-NaCl, transfer RNA or an ion-exchange resin, can be cleaved by DNAase II only at the internucleosomal cleavage site leading to 200-bp² digestion patterns regardless of the ionic conditions. When H1 was added back to the three chromatin preparations the 100-bp cleavage pattern could be restored only with material prepared by the resin method at low concentrations of salt. Addition of polylysine instead of H1 has the same effect, but only with material prepared by that method. A direct correlation between extended and condensed states of chromatin as monitored by electron microscopy and DNAase II cleavage in the 200 and 100-bp modes, respectively, could be established.The continuity of the nucleosome chains in DNAase II-digested chromatin is maintained in spite of intranucleosomal cleavage in the terminal section of the core DNA, even in the absence of H1. Addition of 3 m-urea, however, disrupts the nucleosome chains at the intranucleosomal cleavage sites and leads to the formation of novel nucleoprotein particles as seen in sucrose gradient centrifugations. Those sedimenting between mononucleosomes and dinucleosomes contain, almost exclusively, DNA of 300 bp (mouse) or 315 bp (chicken erythrocyte). They can be formed from particles sedimenting in the absence of urea in the dinucleosome region by either a dissociation process or a massive conformational change.On the basis of the results presented here and in the preceding paper a mechanism for DNAase II cleavage of chromatin in the 200-bp and 100-bp modes is proposed and discussed in the context of structural features of chromatin recognized by DNAase II.     

Functional half-lives of bacteriophage m13 gene 5 and gene 8 messages.

The half-lives of the M13 gene 5 and gene 8 messages were determined by measuring the decay in the rate of synthesis of the gene 5 and gene 8 proteins after inhibition of new RNA chain initiations with rifampin. The gene 5 and gene 8 messages decay with half-lives of approximately 2.5 and 5 min, respectively. We found no evidence of a functional M13 message with a half-life as long as that reported for hybridizable mRNA.     

Biochemical studies on the esterase enzymes of four species of nemertean worms

Esterase enzymes were studied biochemically in extracts of four species of nemertean worms. Optimal enzymic activity occurs within the range pH 6.0–8.2. The relative amounts of esterolytic activity differ between species and, within individual species, between pH optima. It is possible that these differences may, at least in part, be related both to phylogeny and the pattern of digestive physiology.10⁻² M sodium taurocholate and 10⁻³ M lead nitrate possess mainly inhibitory effects, whereas 10⁻³ M cysteine hydrochloride functions predominantly as an activator. The precise effect in each case depends both upon the species and the pH of incubation.Esterases at pH 7.4 are most active at temperatures within the range 40–51 °C, depending upon the species concerned.     

Cell wall lipopolysaccharide damage in Escherichia coli due to freezing

Freezing and thawing of Escherichia coli in water suspensions produce uninjured, nonlethally injured, and lethally injured cells as determined by their ability to multiply under different conditions. These treatments do not affect the microscope count or the optical density of the suspensions. The nonlethally injured cells develop extreme sensitivity to deoxycholate, lauryl sulfate, actinomycin D, and lysozyme. Lethally injured cells can be lysed by lysozyme as measured by the reduction in microscope count and optical density. These results have suggested that the outer membrane of the cell wall, which acts as a protective barrier in normal cells, has been damaged during freezing. In nonlethally injured cells, the damage can be repaired in K₂HPO₄ solutions. Reduction in the adsorption efficiency of the T-series phages indicated that the lipopolysaccharide, and not the lipoprotein of the outer membrane of the cell wall, is damaged in the frozen cells.     

The effect of spatial heterogeneity on the persistence of predator-prey interactions

The effect of spatially discontinuous environments on predator-prey systems is examined by using a computer simulation model. It is shown that increasing prey dispersal and decreasing predator dispersal do not necessarily have a stabilizing influence on the interaction, as had been concluded by previous workers. The stability of predator-prey interaction depends on the interaction of the dispersal process with normal reproduction and feeding of the predator and prey species.     

On the statistical significance of primary structural features found in DNA-protein interaction sites

Probabilities of occurrence for a number of the symmetries and other sequence regularities found in DNA-protein interaction site sequences have been calculated for segments of random DNA sequence. Results show that many of the symmetrical and repetitive features seen in these interaction sites are likely to have occurred by chance. Other features are so unlikely to have occurred by chance that they are probably involved in the DNA-protein interaction processes.     

Engineering defensin α‐helix to produce high‐affinity SARS‐CoV‐2 spike protein binding ligands

The binding of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) spike protein to the angiotensin‐converting enzyme 2 (ACE2) receptor expressed on the host cells is a critical initial step for viral infection. This interaction is blocked through competitive inhibition by soluble ACE2 protein. Therefore, developing high‐affinity and cost‐effective ACE2 mimetic ligands that disrupt this protein–protein interaction is a promising strategy for viral diagnostics and therapy. We employed human and plant defensins, a class of small (2–5 kDa) and highly stable proteins containing solvent‐exposed alpha‐helix, conformationally constrained by two disulfide bonds. Therefore, we engineered the amino acid residues on the constrained alpha‐helix of defensins to mimic the critical residues on the ACE2 helix 1 that interact with the SARS‐CoV‐2 spike protein. The engineered proteins (h‐deface2, p‐deface2, and p‐deface2‐MUT) were soluble and purified to homogeneity with a high yield from a bacterial expression system. The proteins demonstrated exceptional thermostability (Tm 70.7°C), high‐affinity binding to the spike protein with apparent K _d values of 54.4 ± 11.3, 33.5 ± 8.2, and 14.4 ± 3.5 nM for h‐deface2, p‐deface2, and p‐deface2‐MUT, respectively, and were used in a diagnostic assay that detected SARS‐CoV‐2 neutralizing antibodies. This work addresses the challenge of developing helical ACE2 mimetics by demonstrating that defensins provide promising scaffolds to engineer alpha‐helices in a constrained form for designing of high‐affinity ligands.