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.     

Homoaconitic Acid Accumulation by a Lysine-Requiring Yeast Mutant

Homoaconitic acid, the second intermediate of the proposed pathway for lysine biosynthesis in yeast, is accumulated in the growth medium of a lysine-requiring mutant. This acid has been identified on paper and column chromatography by comparing it with authentic cis-homoaconitic acid. The infrared spectrum of the isolated material was identical with that of synthetic cis-homoaconitic acid. In addition, the chemical structure of the enzymatic product has been verified by degradation to glyoxylic and α-ketoglutaric acids after treatment with KMnO₄ and HIO₄ and by catalytic reduction to the saturated acid 1,2,4-butanetricarboxylic acid. The isolated homoaconitic acid was also identified as a substrate for a purified enzyme preparation of homoaconitase.     

Book Reviews

Book reviewed in this article:
ARCHEOLOGY: Papers of the New World Archaeological Foundation
No. 6. The Carved Human Femurs from Tomb 1, Chiapa de Corzo, Chiapas, Mexico . P ierre A grinier
No. 7. Archaeological Explorations in the Region of the Frailesca, Chiapas, Mexico . C arlos N avarrete
Nos. 8–11. Excavations at Chiapa de Corzo, Chiapas, Mexico . G areth W. L owe
No. 12. Mound 5 and Minor Excavations, Chiapa de Corzo, Chiapas, Mexico . G areth W. L owe
No. 13. Ceramic Stratigraphy at Santa Cruz, Chiapas, Mexico . W illiam T. S anders
No. 14. The Santa Marta Rock Shelter, Ocozocoautla, Chiapas, Mexico . R ichard S. M ac N eish and F redrick A. P eterson     

Analysis of sequential stages in serum bactericidal reactions

Michael, J. Gabriel (House of the Good Samaritan, Children's Hospital Medical Center, Boston, Mass.), and Werner Braun. Analysis of sequential stages in serum bactericidal reaction. J. Bacteriol. 87:1067-1072. 1964.-The bactericidal reaction of "normal" human serum against Escherichia coli was found to be separable into two distinctive stages. The early (first) stage of the reaction lasts for a relatively short period of time, and involves factors that are present in sufficient amounts only in slightly diluted serum. The later (second) stage needs more time and requires factors present in highly diluted serum. The first stage depends on the presence of Ca(++) and Mg(++) and on the activity of all components of complement; the second stage does not require divalent cations and C'1, C'2, and C'4, but requires factors that can be removed by zymosan. Under our conditions, removal of lysozyme did not influence either stage of the reaction. Bacteria exposed to concentrated serum for a short time, during the first stage, are essentially unaffected as far as their potential for subsequent multiplication is concerned; the actual damage to cellular integrity occurs only during the second stage of the reaction. In the absence of cell division, the "sensitization" produced during the first stage can be preserved for prolonged periods, and the bactericidal reaction can be completed later by exposure to antibody-free, highly diluted serum (second stage). Cell multiplication abolishes the sensitizing effects of the first stage.     

Oriented Embedding of Biological Materials and Accurate Localization for Ultrathin Sectioning

Gelatin capsules with rounded ends clipped off and open ends moistened, affixed to a glass slide and sealed with a 15% gelatin solution are used to embed blocks of tissue in plastic. The surface of the slide serves as an orientation plane for structures of the tissue. The plane end of capsules of polymerized plastic containing no tissue is used in embedding frozen tissue sections. The plastic-infiltrated section is flattened against the capsule end under the weight of a 3/4 inch square of plate glass so that larger sections may be cut and surveyed. Embedding cultured cell monolayers grown on coverslips is accomplished in a comparable manner, but the square of plate glass is not needed as a weight. Block-face localization methods depend on the type of material embedded. With blocks of tissue it is achieved by moistening the face with xylene to develop relief. Thin tissue sections are examined by transmitted light, while cell monolayers are stained on the capsule end with methylene blue.