Untargeted mutagenesis induced by UV in the lacI gene of Escherichia coli

Summary Using a nonselective method, we have estimated the proportion of untargeted mutations in the lacI gene of E. coli by transferring either irradiated or unirradiated F pro lac plasmids from an excision deficient donor to an excision deficient pro lac deleted recipient that had been irradiated and allowed to induce recA dependent functions for 30 min. We find that about 10 percent of the mutations induced by either 3.5 Jm^-2 or 7 Jm^-2 UV are untargeted.     

New mutations affecting induced mutagenesis in yeast

Previously isolated mutations in baker's yeast, Saccharomyces cerevisiae, that impair induced mutagenesis were all identified with the aid of tests that either exclusively or predominantly detect base-pair substitutions. To avoid this bias, we have screened 11 366 potentially mutant clones for UV-induced reversion of the frameshift allele, his4–38, and have identified 10 mutants that give much reduced yields of revertants. Complementation and recombination tests show that 6 of these carry mutations at the previously known REV1, REV1 and REV3 loci, while the remaining 4 define 3 new genes, REV4 (2 mutations), REV5 and REV6. The rev4 mutations are readily suppressed in many genetic backgrounds and, like the rev5 mutation, impart only a limited deficiency for induced mutagenesis: it is likely, therefore that the REV4⁺ and REV5⁺ gene functions are only remotely concerned with this process. The rev6 mutants have a more general deficiency, however, as well as marked sensitivity to UV and an increased spontaneous mutation rate, properties that suggest the REV6 gene is directly involved in mutation induction. The REV5 gene is located about 1 cM proximal to CYC1 on chromosome X.     

The localization of hexokinase isoenzymes in red and white skeletal muscles of the rat

Summary Maximum assayable hexokinase activities vary with the proportion of red, fast-twitch, oxidative-glycolytic and intermediate, slow-twitch, oxidative fibres in different rat skeletal muscles. The major isoenzymic form, type II hexokinase, is present throughout the intermyofibrillar sarcoplasm in all fibres but a proportion of the total activity appears to be weakly associated with mitochondria. Variations in the histochemical staining intensity between fibre types correlate with their mitochondrial content and seem to be due mainly to differences in mitochondrially-associated hexokinase activity. Changes in the strength of this association may be important in controlling increases in glucose metabolism in response to prolonged increased muscular activity while regulation of the equilibrium between free and loosely-bound forms may be an important control feature in all skeletal muscle. Type I hexokinase is a minor isoenzymic component of skeletal muscle and occurs mainly in blood vessels and nerves in the perimysia and endomysia. The majority of this isoenzyme is tightly bound to mitochondria and is not detectable in homogenates prepared in the absence of Triton X-100.     

Identity of the photoproduct that causes lacI mutations in UV-irradiated Escherichia coli.

Estimates of the capacity of photoreactivation to act specifically on premutational lesions were obtained by conjugational transfer of an F' lac plasmid from a UV-irradiated, photoreactivated donor to a delta (pro-lac) recipient that had been UV irradiated and allowed to induce SOS functions for 30 min. This treatment reduced the frequency of induced lacI mutations by 70 to 80%, indicating that cyclobutane dimers cause most mutations in this system.     

Systemic and renal hemodynamic responses to vascular blockade of vasopressin in conscious dogs with ascites

A role for arginine vasopressin has been implicated in the compensatory control of arterial blood pressure in several animal models with reported increases in plasma levels of arginine vasopressin. A threefold elevation in plasma vasopressin has been reported in conscious dogs following constriction of the inferior vena cava. In the present study, infusion of the arginine vasopressin antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-methyltyrosine] Arg8-vasopressin into conscious dogs with chronic caval constriction did not decrease mean arterial blood pressure. However, the dose of infused antagonist completely blocked the pressor response to 2 micrograms of exogenous vasopressin. Also the antagonist produced no effect on heart rate, plasma renin activity, or urinary volume and electrolyte excretions. A slight, transient increase (P less than or equal to 0.05) was observed in creatinine clearance and in PAH clearance following antagonist infusion, suggesting a possible decrease in renal vascular resistance. These data suggest that the direct vasoconstrictor actions of vasopressin contribute minimally, if at all, to blood pressure maintenance following chronic caval constriction. Alternatively, blockade of endogenous vasopressin receptors at the level of peripheral arterioles may have resulted in no depressor response due to a masking of this response by other compensatory hormonal and neural pressor systems.     

Transforming growth factors--an overview

Transforming Growth Factors (TGFs) are a sub-group of a larger family of protein hormones. Two major types of TGF are currently known, alpha-TGF and beta-TGF. Biologically their most important property is to act synergistically to induce anchorage-independent growth of target cells otherwise incapable of such growth. Since this growth parameter is well correlated with tumorigenicity in vivo, these factors may play a role in cancer development. Biochemically both alpha-TGF and beta-TGF have been well characterised in some types of cells and tissues. Their role in normal and neoplastic growth is actively studied.     

Mice coisogenically immunized against H-2 class I antigens on transfected l cells reject transplanted embryonal carcinoma cells

Evidence is presented of the ability of H-2 class I antigens to function as teratocarcinoma transplantation (Gt) antigens. Coisogenic immunization against H-2 class I antigens expressed on transfected L cells is shown to induce resistance to embryonic carcinoma (EC) cell allografts. The K^b, D^b, D^d, and, in appropriate recipients, L^d antigens can function as Gt antigens. The protocol presented may be useful for the molecular identification of other genes encoding histocompatibility antigens.     

The involvement of histone H1[0] in chromatin structure.

Micrococcal nuclease digestion and light scattering are used to compare native chromatins with various histone H1[0] contents. The experimental data show that the higher the H1[0] content, the greater the ability to form compact structures with increasing ionic strength, and the lower the DNA accessibility to micrococcal nuclease. On the contrary, reconstituted samples from H1-depleted chromatin and pure individual H1 fractions behave in such a way that samples reconstituted with pure H1 degree give rise to a looser structure, more accessible to nuclease than samples reconstituted with H1-1. This contradiction suggests that the effect of H1o on chromatin structure must originate from the interaction of this histone with other components in native chromatin among which other histone H1 subfractions are good candidates.     

Comparative sequence analysis as a tool for studying the secondary structure of mRNAs.

Analysis of phylogenetically conserved secondary structure has been important in the development of models for the secondary structure of structural RNAs. In this paper, we apply this type of analysis to several families of informational RNAs to evaluate its usefulness in developing secondary structure models for mRNAs and mRNA precursors. We observed many conserved helices in all mRNA groups analyzed. Three criteria were used to identify potential helices which were not conserved solely because of coding sequence constraints, and may therefore be important for the structure and function of the RNA. These results suggest that this approach will be useful in deriving secondary structure models for informational RNAs when used in conjunction with other complementary techniques, and in designing experiments to determine the functional significance of conserved base pairing interactions.     

Do Chaoborus larvae migrate in temporary pools?

A diurnal vertical migration of larvae of Chaoborus punctipennis (Say) was observed in shallow temporary woodland pools in East Texas. In the laboratory, in 153 cm tall columns, the larvae underwent a much greater migration than possible in the shallow pools. We hypothesize that the migratory behavior and transparent body of Chaoborus larvae may have originally evolved in such shallow water habitats. These traits enabled Chaoborus to successfully invade the quite different adaptive zone of predation in the plankton of deep lakes.