Simian Virus 40 Transformation and the Period of Cellular Deoxyribonucleic Acid Synthesis

The antiviral agents interferon and statolon protected cells of the mouse line 3T3 against the transforming effect of simian virus 40. Loss of ability of these agents to protect when added some time after infection indicated that the transformation was already fixed. The cells of exponentially growing cultures became resistant to the protective effect of interferon at a linear rate after infection; after one cell generation, the whole population was resistant. By use of synchronous cultures, it was shown that, in cells passing though the G-1 period of the growth cycle, the transformation did not pass the interferon-sensitive stage, whereas cells in S [the period of cellular deoxyribonucleic acid (DNA) synthesis] readily passed this stage (i.e., became interferon-resistant). An irreversible step in transformation appeared to occur in cells synthesizing DNA, and it seems likely that replicating cellular DNA was the target of the viral action.     

Thermodynamics of the binding of biotin and some analogues by avidin

1. The reaction between avidin and biotin was found to be exothermic, ΔH being −20·3kcal./mole of biotin bound. The corresponding value of ΔH for streptavidin was −23kcal./mole. 2. The heat evolved was independent of the pH (between 5 and 9), of the buffer (borate or ammonia) and of the fractional saturation of the avidin with biotin. 3. The entropy change for the reaction was zero, and it is suggested that the entropy increase to be expected from hydrophobic interactions was counterbalanced by a decrease in entropy accompanying the formation of buried hydrogen bonds. 4. Modification of the potential hydrogen-bonding sites of the imidazolidone ring led to a decreased heat output and a positive entropy of reaction.     

Measurement by HPLC of Desferrioxamine-Available Iron in Rabbit Kidneys to Assess the Effect of Ischaemia on the Distribution of Iron Within the Total Pool

A method for the determination of desferrioxamine-available iron in tissue fractions is described which involves incubation with desferrioxamine, extraction of desferrioxamine and its iron-bound form, ferrioxamine, and quantitation of these two forms of the drug by reversed-phase hplc analysis. Chelatable iron levels in the 1-10µMolar region could be accurately and reproducibly measured using this technique.

The desferrioxamine-available iron levels in both the cortex and medulla of rabbit kidneys were significantly elevated (up to 2-fold) after the organs had been subjected to 2 hours warm ischaemia or 24 hours cold storage at 0°C In hypertonic citrate solution. There was no change in the total iron content of the tissues under these circumstances and thus a redistribution of intracellular iron to more available pools had presumably taken place as a result of ischaemia. This redistribution of iron may be an important factor in the initiation of peroxidative damage to cell membranes upon reperfusion of the organ with oxygen.     

Guanylyl cyclase is a heat-stable enterotoxin receptor.

Plasma membrane forms of guanylyl cyclase have been shown to function as natriuretic peptide receptors. We describe a new clone (GC-C) encoding a guanylyl cyclase receptor for heat-stable enterotoxin. GC-C encodes a protein containing an extracellular amino acid sequence divergent from that of previously cloned guanylyl cyclases; however, the protein retains the intracellular protein kinase-like and cyclase catalytic domains. Expression of GC-C in COS-7 cells results in high guanylyl cyclase activity. In addition, heat-stable enterotoxin from E. coli, but not natriuretic peptides, causes marked elevations of cyclic GMP and is specifically bound by cells transfected with GC-C. The enterotoxin fails to elevate cyclic GMP in nontransfected cells or in cells transfected with the natriuretic peptide/guanylyl cyclase receptors. These results show that a heat-stable enterotoxin receptor responsible for acute diarrhea is a plasma membrane form of guanylyl cyclase.     

The molecular analysis ofbrown eye color mutations isolated from geographically discrete populations ofDrosophila melanogaster

A large proportion of spontaneous mutations inDrosophila melanogaster strains of laboratory origin are associated with insertions of mobile DNA elements. As a first step toward determining whether spontaneous laboratory mutations are predictive for mutational events occurring in the wild, recessivebrown (bw) eye color mutants were isolated. By inbreeding the progeny of wild-caughtDrosophila melanogaster females,bw mutations were isolated from seven separate geographic sites distributed among Japan, California, Siberia and Hungary. Among a total of 14 mutations studied, no case of transposon mutagenesis was found. At least 4 mutations are associated with small deletions in thebw gene. The remainder are inseparable from wild-typebw by Southern analysis and are presumed to be basepair changes or very small indels. Although only two spontaneousbw mutants of laboratory origin have been analyzed molecularly, one is a mobile element insertion.