Comparison of glucokinase in C3H/He and C58 mice that differ in their hepatic activity

Partially purified preparations of the hepatic glucokinase from C3H/He and C58 inbred mice have been used to explore the molecular basis for the observed twofold difference in activity between the strains. The single codominant gene that appears to regulate activity, the alleles of which are designated Gk^a and Gk^b, respectively, for the two strains, could represent a structural gene change. This now seems unlikely because the mouse enzyme, although showing small differences from rat glucokinase, appeared to be identical in the two strains with respect to thermal stability, electrophoretic mobility in agarose gels, and kinetic properties such as the apparent K _m values for MgATP^2– and glucose and the unique cooperative interaction with the latter substrate. The enzymes also reacted identically in a range of immunological tests (double-diffusion, immunoelectrophoresis, immune precipitation and immune inhibition assays) and ELISA immune inhibition assays indicated that the twofold difference in activity was due to a similar difference in antigenically active enzyme. Genetic control over the physiologically significant regulation of enzyme amount is therefore probable.This work has been supported in part by a grant from the British Diabetic Association and a Training Studentship to PAJ from the Medical Research Council (U.K.).     

Distribution of Alginate Lyase Activity among Strains of Bacillus circulans

Strains from four different DNA relatedness groups of Bacillus circulans showed apparent alginate lyase activity; the activity of three strains examined had mannuronidase specificity. A representative strain of group 4 also produced apparent inducible unsulfated chrondroitin lyase activity.     

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.     

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.     

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.