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.     

Modification of the zona-free hamster ova bioassay of boar sperm fertility and correlation with in vivo fertility

These studies were designed to evaluate the ability of the zona-free hamster ova bioassay to detect differences in fertility of boar sperm. In the first study, sperm from two previously infertile boars were compared to sperm from seven previously fertile boars. The percentage of zona-free hamster ova penetrated by sperm from the previously infertile boars was significantly lower than the percentage of ova penetrated by sperm from previously fertile boars (18% of ova penetrated vs. 83%, P < .001). In the 14 ejaculates from the previously infertile boars that had ejaculate motilities of 50% or greater, the percentage of zona-free hamster ova penetrated continued to be lower than in ejaculates from the fertile boars. One of the two previously infertile boars consistently had a normal semen analysis. The only two observed manifestations of his reduced fertility were his zero conception rate and the limited ability of his sperm to penetrate zona-free hamster ova. In the second study, females were inseminated with equal numbers of sperm from two previously fertile males and the paternity of offspring determined at birth. The experiment was replicated with four combinations of six boars. A high correlation was observed between the percentage of offspring sired and the ability to penetrate zona-free hamster ova (R = .89). Neither morphology nor the ability of the sperm to undergo an acrosome reaction during in vitro incubation was correlated with fertility in the competitive mating situation. These results suggest the zona-free hamster ova bioassay can improve the in vitro fertility assessment of fresh boar semen.