Interaction of the exr and lon Genes in Escherichia coli

Strains of Escherichia coli carrying the gene lon typically produced excess capsular polysaccharide, and were sensitive to ultraviolet light (UV) irradiation, thymine starvation, and nalidixic acid, forming long filaments after these treatments. Sensitivity was reduced by a number of posttreatments. In the presence of a second UV sensitivity gene, exr, some of these properties were suppressed: long filaments were not formed, the effect of lon on UV and nalidixic acid sensitivity was greatly reduced, and irradiation posttreatments gave an enhancement of survival characteristic of exr rather than lon strains. Production of capsular polysaccharide was not affected by the exr gene.     

Effects of Ionizing Radiation on Synchronous Cultures of Escherichia coli B/r

The sensitivity of Escherichia coli B/r to X-irradiation is correlated with the replication cycle of deoxyribonucleic acid (DNA). The sensitivity to X-irradiation in the wild type can be attributed to the presence of nuclear targets plus DNA repair mechanisms. The effects of nuclear targets are observed in the recombination-deficient (rec−) mutant B/r, but the sensitivity reflected by changes in the slope of killing curves is absent. A study of different growth conditions indicates that maximal resistance to X rays occurs toward the middle of the division cycle. Evidence is offered that branched chromosomes respond as one-hit targets to X-irradiation. The killing effects of heavy-ion bombardment on E. coli are due primarily to ionizing radiation.     

Deoxyribonucleic Acid Synthesis During Microcyst Germination in Myxococcus xanthus

Deoxyribonucleic acid (DNA) synthesis was measured during microcyst germination in Myxococcus xanthus by radioactive thymidine incorporation, autoradiography, and chemical analysis. Microcysts contained an average of 6.6 conserved units of DNA, corresponding to 3 to 4 chromosomes per cell. Correlation of the DNA content and chromosome number of microcysts indicated that the molecular weight of the nonreplicating M. xanthus chromosome is 4.9 x 10(9) daltons. DNA synthesis was initiated 3.5 to 4 hr after induction of germination. From 4 to 6 hr, the rate of synthesis was constant and the accumulation was linear. After a lag period (6 to 6.5 hr), the rate of DNA synthesis increased, reaching a second plateau at 9 hr. From 9 to 11 hr, the rate was again constant and the accumulation was linear. Cellular division during germination showed an unusual kind of synchrony. A model is presented that accounts for chromosomal replication and cell division during microcyst germination.     

Distribution of β-thalassemia trait and erythrocyte glucose-6-phosphate dehydrogenase deficiency in the Markham river valley of New Guinea

Ten villages in or near the Markham Valley, northeastern New Guinea, have provided a sample of 476 males for the ascertainment of glucose-6-phosphate dehydrogenase (G6PD) deficiency and 810 individuals of both sexes for the investigation of the β-thalassemia trait. An extreme heterogeneity was found in the prevalence of both traits when the villages were analyzed separately (from 1.5% to 18.2% demonstrating G6PD deficiency and from 0 to 22.8% evincing β-thalassemia trait). The latter result counters an earlier report from the same region that β-thalassemia trait frequencies correlated negatively with altitude and (presumably) positively with endemicity of malaria. The present findings, based on a more representative sample, do not necessarily invalidate the relationship between malaria and β-thalassemia trait suggested by earlier studies, but they do make clear that correlation in New Guinea, at least, may be complicated by random genetic drift, although other possibilities are discussed. The heterogeneous distribution of G6PD deficiency in the present study confirms similar earlier findings. The importance of sample provenience and anthropological data in the interpretation of differences in the distribution of genetically determined traits is stressed.     

Influence of Relative Humidity on the Survival of Some Airborne Viruses

A system for studying the effects of relative humidity (RH) and temperature on biological aerosols, utilizing a modified toroid for a static aerosol chamber, is described. Studies were conducted at 23 C and at three RH levels (10, 35, and 90%) with four viruses (Newcastle disease virus, infectious bovine rhinotracheitis virus, vesicular stomatitis virus, and Escherichia coli B T3 bacteriophage). Virus loss on aerosol generation was consistently lower at 90% than at 10 or 35% RH. When stored at 23 C, Newcastle disease virus and vesicular stomatitis virus survived best at 10% RH. Infectious bovine rhinotracheitis virus and E. coli B T3 bacteriophage survived storage at 23 C best at 90% RH.     

MICROSPECTROPHOTOMETRIC ANALYSIS OF NUCLEAR DNA IN CHARA ZEYLANICA

Microspectrophotometric analysis of the DNA content of nuclei in various parts of Chara zeylanica Willd. revealed that the amount of DNA in the nucleus of an internodal cell equals twice the amount of DNA in the nucleus of a sperm, while the half-anaphase stage of the same nodal cells contains the same amount of DNA as the nuclei of the male gametes. The DNA content of the nuclei of internodal cells may rise as much as 50 times higher than that of the gametes. However, in the oldest (most basal) internodal cells, the DNA content of the minute nuclei falls again to the basic (1 C) amount. Measurements of sister nuclei derived by amitosis indicated that both nuclei have equal amounts of DNA; this was interpreted as further evidence that amitosis is not a disorganized process or manifestation of degeneration. The bearing of these analyses on the question of the site of meiosis in these plants is discussed.     

An Ion Displacement Membrane Model

The usual assumption in treating the diffusion of ions in an electric field has been that the movement of each ion is independent of the movement of the others. The resulting equation for diffusion by a succession of spontaneous jumps has been well stated by Parlin and Eyring. This paper will consider one simple case in which a different assumption is reasonable. Diffusion of monovalent positive ions is considered as a series of jumps from one fixed negative site to another. The sites are assumed to be full (electrical neutrality). Interaction occurs by the displacement of one ion by another. An ion leaves a site if and only if another ion, not necessarily of the same species, attempts to occupy the same site. Flux ratios and net fluxes are given as functions of the electrical potential, concentration ratios, and number of sites encountered in crossing the membrane. Quantitative comparisons with observations of Hodgkin and Keynes are presented.     

Effects of a Single Histoplasmin Skin Test on the Serological Diagnosis of Histoplasmosis

Numerous reports have indicated that a single histoplasmin skin test may stimulate humoral antibodies to Histoplasma capsulatum antigens in histoplasmin-hypersensitive individuals. Although these investigations concur that antibody elevations are evoked, they vary in the reported degree of incidence and response induced, and they cast doubt on the interpretation of serological tests in the diagnosis of histoplasmosis. Histoplasmin-hypersensitive subjects (114) were bled prior to administration of the skin test, 2 days later, at the time this test was read, and 15 and 30 days after testing. No significant antibody titers were observed at 2 days. At 15- and 30-day intervals, only 17 (15%) of the subjects demonstrated circulating antibodies. All 17 showed agar gel bands; 5 demonstrated no complement-fixation (CF) titers, 10 produced CF antibodies ranging from 1:8 to 1:16, and 2 demonstrated titers of 1:32. The data suggest that skin testing does not interfere significantly with antibody levels in sera drawn approximately 2 days after administration of antigen. However, since titers as high as 1:32 were obtained at later intervals, such reactions should be evaluated cautiously and only after consideration of clinical findings.