Linear, Single-Stranded Deoxyribonucleic Acid Isolated from Kilham Rat Virus

Kilham rat virus (KRV) was grown in a rat nephroma cell line and was purified by two isopycnic centrifugations in cesium chloride. The virus contains single-stranded deoxyribonucleic acid (DNA) with a molecular weight of approximately 1.6 x 10(6). The DNA was extracted from the virion by both phenol extraction and by 2% sodium dodecyl sulfate at 50 C. KRV DNA, extracted by both procedures, was observed in an electron microscope by using a cytochrome c or diethylaminoethyldextran monolayer. The DNA was also exposed to exonuclease I, an enzyme which hydrolyzes specifically linear, single-stranded DNA. Hydrolysis of 70 to 80% of the DNA was observed. Both the enzymatic and the electron microscope studies support the conclusion that extracted KRV DNA is a single-stranded, linear molecule. The length of the DNA was measured in the electron microscope and determined to be 1.505 +/- 0.206 mum.     

Metabolic Regulation by Homoserine in Escherichia coli B/r

A mathematical analysis of branched pathway regulation has led to the prediction of a novel homoserine control in Escherichia coli B. Experimental support for such control is presented in this paper. Homoserine, the precursor of both threonine and methionine, inhibits nicotinamide adenine dinucleotide phosphate (NADP(+))-specific glutamate dehydrogenase (EC 1.4.1.4), the enzyme catalyzing the first reaction in ammonia assimilation. Physiological and biochemical evidence for this effect are offered. Homoserine depresses the growth rate of the organism, and glutamate, the product of the inhibited reaction, reverses this effect. The NADP(+)-specific glutamate dehydrogenase activity in cell-free extracts is inhibited by homoserine, and this inhibition parallels the restriction of growth rate. These effects are found in other enteric bacteria which share a similar overall pattern of control for the amino acids derived from aspartate. On the other hand, a sampling of more distantly related species which have different pathways and/or regulatory patterns provides no evidence for homoserine inhibition of the glutamate dehydrogenase reaction.     

The Fertility of Melanesian Girls, Laboratory Mice, and Prostitutes: A Comment on the "Bruce Effect"

Greenfield has recently proposed that low fertility in both prostitutes and unmarried Trobriand girls may be explained by the "Bruce effect": the inhibition of pregnancy in female mice that have had intercourse with different males within a short period. An examination of Malinowski's data indicates that a Trobriand girl usually had intercourse with only one man over a fairly long period and her sex life was not at all comparable to that of a prostitute or one of Bruce's mice. Low fertility in unmarried girls has been well documented for several Melanesian societies that differ notably in the behavior permitted to girls. The existence of so-called adolescent sterility still seems to be the best explanation to cover all of these cases. [fertility, sexual behavior, Melanesia]     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.     

Modified Microbiological Assay for Rapid Estimation of Antibiotic Concentrations in Human Sera

Antibiotic concentrations in human sera were estimated in 5 to 6 hr by a modified microbiological assay. By using Staphylococcus aureus and Streptococcus pyogenes as the assay organisms, the seeded assay plates were preincubated for 2 to 6 hr and then were stored at 4 C until used for assay. Paper discs saturated with the specimen were placed on the preincubated assay plates with reference discs saturated with known concentrations of antibiotic. After 5 to 6 hr of incubation, zones of antibacterial activity were measured and compared with a standard curve for estimation of antibiotic concentration. Results from this rapid assay method compared favorably with those from the commonly used 24-hr assay.     

A Survey of Infantile Gastroenteritis

In 1967 we admitted 339 cases of infantile gastroenteritis; one-third of these were dehydrated, and in this group the commonest biochemical abnormality found was hypernatraemia, sometimes with metabolic acidosis. A higher incidence of dehydration was found in the patients who had received oral glucose fluids before admission. Enteropathic Escherichia coli were isolated from the faeces of 16% of the cases. Associated infections, especially of the respiratory tract, were common. Treatment was aimed at the restoration of fluid and electrolyte balance. Usually this was achieved with oral fluids, though intravenous fluids were used in the most severely dehydrated cases. Recovery was complete in 320 cases and a further 14 cases were discharged as carriers of enteropathic E. coli. There were five deaths (1·5%) in the series; three occurred immediately after admission.