The exchange hypothesis for the formation of chromatid aberrations: an experimental test using bleomycin

The association between bleomycin-induced chromatid aberrations and BUdR-label exchange between sister chromatids was investigated in order to evaluate Revell's exchange hypothesis for the formation of chromatid aberrations. The results of this study indicate that a larger than expected proportion of chromatid breaks can be accounted for by the exchange hypothesis though not all breaks are the result of incomplete exchange.     

Isolation and Characterization of Temperature-Sensitive Mutants of Vesicular Stomatitis Virus, New Jersey Serotype

Forty-eight temperature-sensitive (ts) mutants have been isolated from a wild-type strain of the New Jersey serotype of vesicular stomatitis virus (VSV) after exposure to the base analogue mutagen 5-fluorouracil. Of these mutants, 47 have been classified into 6 nonoverlapping complementation groups containing 21, 17, 4, 3, 2, and 1 mutant, respectively (1 mutant remaining unallocated). The ribonucleic acid (RNA) phenotype of 23 of these mutants has been established. Four of the six groups contain one or more mutants unable to synthesize detectable amounts of viral RNA under restrictive conditions (39 C). No complementation was observed in mixed infection with ts mutants from the five established complementation groups of the Indiana serotype of VSV.     

Substituted Sialic Acid Prosthetic Groups as Determinants of Viral Hemagglutination

Inhibitors of hemagglutination by type A2 influenza virus and a recently isolated strain of type B influenza virus were separated by sucrose density gradient centrifugation and agarose gel filtration from horse serum. Using selected reagents, it was demonstrated that the active substituent on the horse serum inhibitor of A2 influenza virus was 4-O-acetyl-N-acetylneuraminic acid; however, the active substituent on the inhibitor of the influenza B virus was shown to be N-acetylneuraminic acid (NANA). Sodium metaperiodate treatment of a component of horse serum resulted in a 10 to 15-fold enhancement of inhibitory activity against the type B virus, whereas the A2 inhibitor was completely destroyed. Since this enhancement did not occur with influenza B viruses isolated prior to 1965, it was considered that this sensitivity to an oxidized NANA glycoside may have been a reflection of an antigenic change which occurred at that time. The use of different virus strains and selected chemical reagents to define the important sialic acid prosthetic groups active in inhibition was described.     

Evidence implicating a membrane ATPase in the control of passive permeability of excitable cells

The temperature sensitivity of the ATPase enzyme systems in a muscle microsomal preparation from the crayfish, Astacus pallipes, was studied. Preincubation of the enzyme preparation in the range 33–36°C produced a marked inactivation of the ATPases; the Mg⁺⁺-dependent ATPase was very much more sensitive to this treatment than the Na⁺-K⁺-Mg⁺⁺-dependent ATPase. Thus, the Arrhenius μ for the inactivation of the Mg⁺⁺-dependent ATPase produced by eight minute preincubation is > 100 Kcals. These results are compared with the changes that are observed during the heat death of the whole animal, where exposure to 35°C produces a dramatic change in Na⁺ permeability within five minutes. Arrhenius μ for heat death is also > 100 Kcals and operates over the identical critical temperature range. It is suggested that the Mg⁺⁺-dependent ATPase controls passive permeability in these excitable cells and the results also confirm the view that Mg⁺⁺ and Na⁺-K⁺-Mg⁺⁺ ATPases are separate enzymes.     

ARAGONITE IN HALIMED A AND TYDEMANIA (ORDER SIPHON ALES)12

The mineral component of the marine green algal genus Halimeda is the orthorhombic calcium carbonate (aragonite); its presence appears to be a generic characteristic. Tydemania expeditionis also precipitates aragonite in contradistinction to species of the red alga Corallina wliich precipitate calcium carbonate of the hexagonal form (calcite). The analyses are based on x-ray diffraction methods. Although other inorganic substances arc present, the amounts are minor and probably represent contaminants. Specimens that are to be studied for mineral components should not be stored in formalin.     

Hospital Infections Caused by a Group of Recently Recognized Strains of Staphylococcus aureus

A survey was made of the phage-types of staphylococci responsible for cross-infection in a large veterans'' hospital between 1961 and 1964. An earlier survey had shown that in 1959 most of the infections were caused by staphylocci of the “80/81/82” group. In 1961 a new group of staphylococci were first recognized and provisionally designated as “Atypical Group III” strains; these were non-typable by the usual typing phages but showed inhibition patterns with some of the Group III phages. The “Atypical Group III” staphylococci all showed one or other of four patterns of multiple antibiotic resistance. By 1963 these resistant “Atypical Group III” staphylococci had become more frequent than “80/81/82” strains as causative agents of cross-infection, although both groups have continued to cause infections in the hospital. “Atypical Group III” strains mainly infected surgical wounds and skin ulcers, whereas “80/81/82” strains commonly produced primary skin sepsis, such as boils.