Biosynthesis of methionine in an ethionine-resistant strain ofCandida utilis

The strainCandida utilis T 20 adapted to a high concentration of ethionine, excretes considerable amounts of methionine in a synthetic medium, about 40 times as much as the original non-adapted strain. At the same time, the amount of methionine in yeast cells incrncreased, predominantly in the pool (9 times as much as in the control). This ability to produce greater amounts of methionine in the pool or to excrete it into the medium is not permanent, since after 5 passages on agar with ut ethionine the amount of methionine was practically not increased as compared with the original non-adapted strain. An increase in free methionine and of methionine excreted into the medium was found on cultivating the strain in a molasses-containing medium, too.     

Biosynthesis of Alkali Insoluble Polysaccharide from UDP-d-Glucose with Particulate Enzyme Preparations from Phaseolus aureus

A particulate enzyme system from Phaseolus aureus seedlings catalyzes the synthesis of alkali insoluble polysaccharide material from UDP-d-glucose. 80 to 90% of the d-glucose units are joined by β-1,4 linkages, the remainder being combined by β-1,3 linkages. It is not known whether the material is a single polysaccharide or a mixture.     

Purification and Chemistry of Bacteriophage ?

From a stock of varkappa phage grown on Salmonella, a host-range mutant which attacks Escherichia coli was isolated. As in the case of Salmonella, only motile strains of E. coli are sensitive to varkappa. The phage shows an eclipse period of 35 min and a minimal latent period of 52 min. The adsorption rate constant is 3 x 10(-9) ml/min. Adsorption shows a marked dependence on temperature. Bacteriophage varkappa was purified by differential centrifugation and CsCl density gradient centrifugation. It contains deoxyribonucleic acid (DNA) which is double-stranded. The DNA has a molecular weight of 42 million and a guanine plus cytosine content of 57%. Of 68 molecules of DNA inspected, 7 were circular. The phage particle weight is about 90 million.     

The homogenous γG-immunoglobulin produced by mouse plasmacytoma 5563 and its subsequent heterogeneity in serum

The mouse plasma cell tumour 5563 has been shown to synthesize and secrete a single molecular species of gammaG-immunoglobulin, which was identified by labelling with (14)C-labelled amino acids. The heterogeneity of G-myeloma globulin as it is found in serum of tumour-bearing mice is due to subsequent changes in the charge properties of the newly secreted molecules. These changes have been reproduced in vitro. On incubation with sterile serum, the newly formed radioactive myeloma protein changed its chromatographic and electrophoretic properties to coincide with those of myeloma protein isolated from serum. Incubation of purified myeloma protein band a, under a variety of conditions, led to the characteristic pattern of serum myeloma protein showing multiple electrophoretic bands. The chemical nature of the molecular changes is not yet known. It is suggested that seruminduced changes could contribute to the electrophoretic heterogeneity of specific antibodies within the gammaG-class of immunoglobulins. This demonstration of the production of a single molecular species of immunoglobulin by a plasma cell tumour provides support for the concept of ;one-cell-one antibody'.     

Electro-optical studies of conformation and interaction of polynucleotides

Measurements by the technique of electric birefringence with pulsed sinusoidal electric fields on polyriboadenylic acid (poly-A) and polyribouridylic acid (poly-U) indicate that the kinetics of the double-stranded helix formation of poly (A + U) in the presence of Mg²⁺ is second order and consists of two steps: nucleation and propagation of base pairs from nuclei. The nucleation involves approximately 7 base pairs. It seems that the requirement of 7 base pairs to start the formation of a double-stranded helix is not peculiar to poly (A + U) but is associated with double-stranded helices of polynucleotides in general. This implies that it may be associated with spatial requirements of the phosphate-sugar backbone, rather than with the particular bases linked to the backbone. The decline in rate of poly (A + U) formation observed above a critical temperature is the consequence of changes in the poly-A conformation setting in at this critical temperature, rather than resulting from an increase in the reversibility of the base-pair propagation step of double-stranded helix formation. The dominant role of the conformation of poly-A in the double-stranded helix formation of poly (A + U) is further borne out by the pH dependence of the rate which completely parallels the conformation changes known to occur in poly-A as a function of pH. This indirectly suggests that at neutral pH poly-A is a single-stranded helix. The rotary diffusion coefficients attest to the flexibility of this helix, while the stacked nature of the base pairs at low temperatures is revealed by the identical increments in the specific Kerr constant on going from poly-A to poly (A + U) and from poly (A + U) to poly (A + 2U) helices. Results suggest that Mg²⁺ binds to the phosphate part of the backbone. Poly-U binds Mg²⁺ more strongly than poly-A; this difference in binding strength is attributed to differences in conformation (random coil versus helix). It is also borne out by the present results that the degree of order in the structure of poly-U, even at low temperatures and neutral pH, is at best an order of magnitude smaller than that of poly-A under similar conditions. Furthermore, the earlier proposed double-stranded structure of poly-U is called into question. A hairpinlike structure seems to agree with results of this investigation. Finally, the results support the contention that the ion atmosphere polarization is responsible for orientation of polyelectrolytes in the presence of alternating electric fields in the neighborhood of 25 kc./sec. frequency.