Ultraviolet Mutagenesis and Its Repair in an ESCHERICHIA COLI Strain Containing a Nonsense Codon

Ultraviolet mutagenesis and its repair were studied mainly in WU36-10-89, a uvr(-) strain of Escherichia coli containing a UAG mutation in a gene for leucine biosynthesis. Following ultraviolet (UV) irradiation revertants appearing with or without direct photoreactivation (PR) were classified according to the presence and type of suppressor they contained. We find UV mutation production to be quite specific. An analysis of revertants produced by UV indicates they are formed mainly from GC --> AT and that the miscoding is due to a cytosine residue at the site of mutation in a cytosine-thymine (CT) dimer. We propose that the dimer serves as template during some aspects of repair replication and at the time of replication the C in the dimer directs the insertion of A in the complementary strand. We also note that C --> A and T -->G changes caused by a CT dimer occur much less frequently.     

On the carbohydrate—protein linkage group in vitreous humor hyaluronate

Fractional molar ratios of serine, threonine and aspartic acid to neutral sugars in the purified bovine vitreous humor hyaluronate, and a 4–5-fold increase in the percentage of these amino acids and the absence of sugar alditols in hyaluronate reduced with NaBH₄---PdCl₂ after alkali treatment indicated the absence of a carbohydrate—protein linkage. Gel filtration behavior, a decrease in intrinsic viscosity of reduced hyaluronate to about one-half and a significant decrease in its specific rotation suggested that the two antiparallel chains of the hyaluronate double helix may come apart upo reduction. The vitreous humor hyaluronate contained 109.2 ppm of “bound” silicon. It is suggested that the bound silicon may bridge the two antiparallel chains through the neutral sugars and/or through the hydroxyl group of the uronic acid moiety.     

X-Ray Diffraction Pattern from a Bilayer with Protein Outside

The X-ray diffraction pattern from a lipid bilayer has been reported previously; a series of fairly regularly spaced bands was both predicted and observed. In this note it is predicted that adding protein molecules at one or both surfaces of the bilayer will give rise to a cross-interference effect. For smaller amounts of protein, a more or less obvious ripple will be introduced into the bilayer pattern. The amount of protein, its thickness, and the distance from the bilayer to the protein layer all can be readily estimated from an observed ripple. Deciding whether the protein is all on one side or else distributed on both sides of the bilayer may be more difficult; by carefully recording and measuring the intensity near the center of the pattern one may be able to distinguish between the two possibilities. For larger amounts of protein, there will be more profound changes in the diffraction pattern. The theory developed here is applied in the following paper to a lipid dispersion incubated with cytochrome c and will be applied in a subsequent paper to a bacterial envelope. In an appendix it is shown that the patterns reported previously for several natural membranes do not confirm prediction for a normal, continuous lipid bilayer with all the protein outside. Thus it is doubtful that a structure of this kind is valid for these membranes.     

CHANGES IN FINE STRUCTURE DURING SILK PROTEIN PRODUCTION IN THE AMPULLATE GLAND OF THE SPIDER ARANEUS SERICATUS

The ampullate silk gland of the spider, Araneus sericatus, produces the silk fiber for the scaffolding of the web. The fine structure of the various parts of the gland is described. The distal portion of the duct consist of a tube of epithelial cells which appear to secrete a substance which forms the tunica intima of the duct wall. At the proximal end of the duct there is a region of secretory cells. The epithelium of the sac portion contains five morphologically distinct types of granules. The bulk of the synthesis of silk occurs in the tail of the gland, and in this region only a single type of secretory droplet is seen in the epithelium. Protein synthesis can be stimulated by the injection of 1 mg/kg acetylcholine into the body fluids. 10 min after injection, much of the protein stored in the cytoplasm of the epithelial cells has been secreted into the lumen. 20 min after stimulation, the ergastoplasmic sacs form large whorls in the cytoplasm. Protein, similar in electron-opacity to protein found in the lumen, begins to form in that portion of the cytoplasm which is enclosed by the whorls. The limiting membrane of these droplets is formed by ergastoplasmic membranes which lose their ribosomes. No Golgi material has been found in these cells. Protein appears to be manufactured in the cytoplasm of the tail cells in a form which is ready for secretion.     

On the morphology,behaviour and systematic status of the assam macaque (Macaca assamensis McClelland, 1839)

Studies on a living and freshly dead male ofM. assamensis at Y.R.P.R.C. supplemented by notes on a living pair and their male offspring observed at the Z.S.L., enable us to supplement existing data on the somatology, craniology, dental anatomy and behavioural features of the species. Collectively the new data necessitate taxonomic revision of the status of the species, viz: its removal from immediate association withM. mulatta (subgenusMaimon) and alignment within the subgenusZati. Zoogeographical discontinuity in this subgenus is compared with that of the subgenusSilenus.     

Cytochemical and ultrastructural studies of ribonucleoprotein containing structures in oocytes of Acheta domesticus

Summary Two distinct types of ribonucleoprotein containing structures are found in oocytes of the house cricket, Acheta domesticus, a large secondary or accessory nucleolus and many small primary nucleoli. The secondary nucleolus increases in size during oocyte development and is similar in appearance to the nucleolus of somatic cells. The primary nucleoli are intimately associated with a large, extrachromosomal DNA containing body. The DNA body is no longer visible in nuclei of late diplotene stage cells when the primary nucleoli are dispersed within the nucleoplasm. Both types of nucleoli contain cytochemically detectable RNA and acid protein, little or no DNA and basic protein, and particulate structures similar to but smaller than cytoplasmic ribosomes.The authors acknowledge the technical assistance of Miss Celeste Malinoski and Mrs. Marcia Andrews. This work was supported by a U.S.P.H.S. grant, number GM-16440-01 and grants number L-16 and J-1 from the Health Research Services Foundation.