Dark Repair of Ultraviolet-Irradiated Deoxyribonucleic Acid by Bacteriophage T4: Purification and Characterization of a Dimer-Specific Phage-Induced Endonuclease

The purification and properties of an ultraviolet (UV) repair endonuclease are described. The enzyme is induced by infection of cells of Escherichia coli with phage T4 and is missing from extracts of cells infected with the UV-sensitive and excision-defective mutant T4V(1). The enzyme attacks UV-irradiated deoxyribonucleic acid (DNA) containing either hydroxymethylcytosine or cytosine, but does not affect native DNA. The specific substrate in UV-irradiated DNA appears to be pyrimidine dimer sites. The purified enzyme alone does not excise pyrimidine dimers from UV-irradiated DNA. However, dimer excision does occur in the presence of the purified endonuclease plus crude extract of cells infected with the mutant T4V(1).     

Pressurized freezing for retarding shrinkage after drying: a quantitative interpretation

Certain gases, when dissolved at high pressure in foods and biological materials, give a structure of gas bubbles inflating cells after freezing, depressurization, and thawing. This phenomenon has been found to reduce shrinkage after subsequent drying. The effect is interpreted quantitatively in terms of the needs for (a) a sufficient solubility of the gas in the water of the tissue at high pressure so that the Bunsen coefficient is high enough (at least 1.5 cm³/cm³ for maximum effect), and (b) a sufficiently low permeability, expressed as the product of atmospheric solubility and diffusivity in water (equal to or less that of air for maximum effect).     

Dihydrofolate reductase: low-resolution mass-spectrometric analysis of an elastase digest as a sequencing tool (Short Communication)

An elastase digest of a protein of unknown structure, dihydrofolate reductase, was studied by mass spectrometry. This soluble digest contained a large number of small peptides in different yields, within the ideal molecular-weight range (200-1200) for mixture-analysis mass spectrometry. Sequences of the major component peptides in the digest are reported.     

Effects of antiepileptic drugs on brain energy reserves during convulsions

Cerebral cortical ATP, P-creatine, glucose, and lactate were measured 6 sec after 1 sec of 150/sec rectangular pulses, at 0,20 v, 40 v, 60 v, 80 v, or 100 v, applied to the heads of intact mice which had been given either no drug, phenobarbitone (25 mg/kg), trimethadione (600 mg/kg), or diphenylhydantoin (40 mg/kg), intraperitoneally. In general, regardless of stimulus strength or drug used, animals which exhibited maximal (tonic-clonic) convulsions showed similar striking decreases in brain P-creatine, decreases in ATP and glucose, and increases in lactate. On the other hand, in animals which exhibited less than maximal clinical response, there was little or no change in these metabolites. An exception was the case of diphenylhydantoin. Tonic-clonic seizures did not occur after diphenylhydantoin administration, even with 100 v stimuli, but substrate changes at this voltage were, nevertheless, similar to those observed in brains of other mice undergoing maximal convulsions.     

The structure and possible mode of functioning of the female reproductive system in Nasonia vitripennis (Hymenoptera: Pteromalidae)

Associated with the female insect reproductive system are a number of glands. Those present in Nasonia vitripennis are described, their microanatomy examined and where possible this is linked with their function during the process of drilling into the host puparium, feeding on the host fluids and oviposition. The structures dealt with are the ovaries, spermatheca, alkaline gland, colleterial gland and the acid gland with reservoir.     

Generic Identification of L-Forms by Polyacrylamide Gel Electrophoretic Comparison of Extracts from Parent Strains and Their Derived L-Forms

A polyacrylamide gel electrophoretic method was used for identification of L-forms in the genera Streptococcus, Staphylococcus, and Proteus, by comparing phenol-acetic acid-water extracts of homologous parent L-form pairs to one another and to other pairs. The method requires only milligram quantities of material for analysis. The standard patterns for the strains used in this study are shown as pictures of the gels and as densitometric tracings of appropriate gels. They show that, despite occasional minor differences in some organisms, the gel electrophoretic patterns of homologous L-forms and bacterial pairs are sufficiently similar-as well as sufficiently dissimilar from patterns of other genera-to permit generic identification of an unknown L-form by reference to patterns derived from possible parental bacteria.