Chi-Stimulated Recombination between Phage λ and the Plasmid λdv

Chi promotes Rec-mediated recombination between phage lambda DNA and the homologous plasmid lambda dv. In the absence of Chi, some of the interactions splice lambda dv into lambda, whereas others patch information from lambda dv into lambda. When Chi is in the phage DNA, splices and patches are increased in frequency by the same factor. This result strengthens the analogy between Chi and recombination-promoting elements in fungi. It also rules out one model for the previously reported orientation dependence of Chi phenotype.     

Yeast mitochondrial and cytoplasmic valyl-tRNA synthetases

Yeast mitochondrial tRNA synthetase has been partially purified and chromatographic, catalytic and antigenic properties have been compared to the cytoplasmic homologous enzyme from yeast. No significant differences could be observed between the two enzymes with respect to their behaviour during ammonium sulfate precipitation or in chromatographic separation on DEAE cellulose, hydroxylapatite and Sephadex G 200. The Km of the two enzymes toward tRNAs from yeast mitochondria, yeast cytoplasm or E. coli are pratically identical. The antigenic properties of the two enzymes are very similar; antisera against either the mitochondria or the cytoplasmic enzyme lead to the inhibition of their catalytic properties. The mitochondrial ValRS is formed by a single polypeptide chain whose molecular weight is 125,000 daltons, a value very close to that of the yeast cytoplasmic enzyme.     

Clonal growth in vitro by mouse Kupffer cells.

Mouse liver Kupffer cells were induced to proliferate and form discrete colonies of mononuclear phagocytes in vitro. These colony-forming cells from the liver are similar to other mononuclear phagocyte colony-forming cells in that they require a colony-stimulating factor present in medium conditioned by L cells for proliferation in vitro. Cells in the colonies were phagocytic and had IgG receptors on the membrane. For this class of colony-forming cells, the D₀ value to gamma irradiation in vitro was 108 rads.     

Inconsistency in the species concept for yeasts due to mutations during vegetative growth

Summary The generic classification of yeasts is based mainly on morphological characteristics whereas the definition of a species depends predominantly on physiological properties such as the utilization of carbon and nitrogen sources. Classification procedures are routinely done on agar slants, and in negative tests single colonies are often noticed. These colonies are spontaneous mutations and can be idetified as such after transfer onto adequate media and appropriate genetic tests. It is sometimes possible after selection steps to obtain a completely different species. This means that in many cases the classification depends only on single gene differences, where the differences in DNA base homology is almost certainly less than 1%. Since it is rather difficult to justify a new species on the basis of a single biochemical gene mutation, it is necessary in practice to perform at regular intervals an extended series of physiological tests in order to avoid confusion in nomenclature.     

Additional evidence for separable responses to auxin in soybean hypocotyl

Additional evidence for two separable responses to auxin is presented. The average of 24 control experiments indicated lag times of 12.4 and 35.4 min, and maximum rates of 0.57 and 0.54 mm hr⁻¹, for the first and second response, respectively. The auxin analog 4-azido-2-chlorophenoxyacetic acid increased the lag time of the second response (but not the first), resulting in the temporal separation of the two responses. Plots of elongation rates against time, taken from the literature, allowed the characterization of the two responses in monocotyls and dicotyls. Study of published rate-time elongation curves showed that the maximum rate of the first response is frequently greater than the maximum rate of the second response; however, the maximum rate of the second response has not yet been shown to exceed the maximum rate of the first response.     

Two elongation responses to auxin respond differently to protein synthesis inhibition

The first and second responses to auxin react differently to the inhibition of protein synthesis by cycloheximide. It was determined that the protein with the shortest half-life, among the several necessary for the first response, is different from its counterpart among the several necessary for the second response. Specifically, the protein half-lives are 28 minutes and 11 minutes for the first and second responses, respectively.     

Clearance of lysosomal hydrolases following intravenous infusion. Kinetic and competition experiments with beta-glucuronidase and N-acetyl-beta-D-glucosaminidase.

Clearance experiments with highly purified lysosomal glycosidases, β-glucuronidase and N-acetyl-β-d-glucosaminidase, following intravenous infusion revealed widely varying clearance profiles which depended on the tissue source of the enzyme. Normal rat serum β-glucuronidase and epididymal N-acetyl-β-d-glucosaminidase were cleared slowly from the circulation when compared with rat preputial gland β-glucuronidase, liver lysosomal β-glucuronidase, and liver lysosomal N-acetyl-β-d-glucosaminidase, respectively, which were cleared rapidly. Experiments comparing the catalytic properties and molecular dimensions of the enzymes revealed no differences between rapid and slow clearance forms. Kinetic analysis using the rapid clearance forms of β-glucuronidase has allowed the resolution of at least two components, rapid and slow. Clearance of the rapid component is saturable and appears to reflect binding or uptake by a limited number of sites. By contrast, the clearance rate of the slow component increased linearly with respect to dose and may be due to nonspecific or low-affinity binding. Competition experiments with β-glucuronidase-free lysosomal extract and highly purified lysosomal enzymes, but not serum glycoproteins or colloidal silver, suggest that one lysosomal enzyme inhibits clearance of others and that a common mechanism may be involved in their binding.