“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.     

Enteric Pathogens in Monkeys

From 1964 to 1967, 6,646 monkeys, representing 10 primate species, were examined for Shigella and Salmonella infections upon arrival at the National Center for Primate Biology. Of these animals, 12% were infected with Shigella, and 75% of the Shigella isolates were S. flexneri 4. The incidence of Salmonella infections decreased from 12 to 3% during the period of study. Epidemiological studies of animals in the colony for 90 days or more indicated no seasonal variation in the occurrence of Shigella and Salmonella. Many of the isolates from incoming monkeys as well as from laboratory-conditioned animals were resistant to chloramphenicol, dihydrostreptomycin, and tetracycline. The possible operation of drug-resistance factors in these infections is discussed.     

ADVANCED NEOPLASTIC DISEASE—Treatment with 5-Fluorouracil and Irradiation

One hundred and twelve patients with far advanced, inoperable neoplastic disease were treated by a method utilizing the simultaneous administration of the pyrimidine antagonist, 5-fluorouracil, and ionizing irradiation to an estimated tumor dose of 2,000 roentgen units. Seventy-seven of them had periods of objective regression of tumor of three months or more.The data presented suggest that either there may be an additive effect when the two modes of therapy are used simultaneously or one mode of therapy may potentiate the antitumor effect of the other.     

HYBRIDIZATION AND CRYPTIC SPECIES IN DICAMPTODON (CAUDATA: DICAMPTODONTIDAE)

The salamander genus Dicamptodon consists of at least four genetically divergent groups of populations with 10–19 fixed allelic differences (out of 31 loci scored) between populations in alternative groups. One of these groups corresponds to D. copei; the other three until now usually have been considered to belong to the single morphologically homogeneous species D. ensatus. Two instances of geographic contact between genetic units occur in the genus, one between D. copei and “D. ensatus” in northern Oregon and the other between two highly divergent types of “D. ensatus” in coastal northern Calfornia. In the former case no hybridization occurs, while in the latter a narrow hybrid zone has been observed. There appears to be selection against hybrids within this hybrid zone, and introgression beyond the zone is apparently nonexistent. The population groups therefore appear to be genetically independent units, and Dicamptodon is best considered to consist of four species: D. copei, D. ensatus, D. tenebrosus, and D. aterrimus.