Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

“Pleiotypic Response”

A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.     

Inhibition of DNA Synthesis but not of Poly-dAT Synthesis by the Arabinose Analogue of Cytidine <Emphasis Type="Italic">in vitro</Emphasis>

Kimball and Wilson¹ reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen² observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators³ had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore⁴ reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler⁵ has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore.     

Endopeptidase Activity of Phage λ-Endolysin

JACOB and Fuerst^1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ³ which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli² and one would therefore expect its substrate to be murein.     

Fine structural study of gas secretion in the physoclistous swim bladder of Fundulus heteroclitus and Gadus callarias and in the euphysoclistous swim bladder of Opsanus tau

Summary The Haldane-Koch-Scholander-Kuhn-Steen theory of salting out countercurrent multiplication effect of the rete mirabile now accounts for release of most gases in the fish swim bladder. Evidence presented here indicates that final release is by microbubbles from the secretory epithelium. There is only one specific cell type in a highly vascularized epithelium. It is characterized by complex folds in the paravascular zone and by gas forming bodies which seem to form from plentiful Golgi material. The bodies are formed with dark amorphous matrix that becomes patterned (tubular or lamellar), finally froths and then is released to the gas surface. Residual material may form myelin-like layers on the lumenal surface. Active cells are also characterized by surface villi and subsurface, parallel cisternal spaces. Gas may be formed by cells not touching the gas surface and released through intercellular spaces. There are discontinuous desmosomes (maculae adhaerentes) near the gas surface and there are no tight junctions (zonulae occludentes). Gas release as bubbles would explain Wittenbergs observations that the gases found in swim bladders have ratios more closely related to their solubility coefficients in water than to ambient partial pressures. A surfactant may be present to lower the surface tension of the microbubbles. The carrier in the cytoplasm would have to be an iron-protein (or perhaps peroxidase) compound capable of binding molecular oxygen.Supported by grant-in-aid from the national Science Foundation (GB-676) and from the USPHS (General Medical Sciences Institute, GM-06836).     

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.