IMP1/imp1: A Gene Involved in the Nucleo-Mitochondrial Control of Galactose Fermentation in SACCHAROMYCES CEREVISIAE

In some strains of Saccharomyces cerevisiae, the induction of enzymes of the Leloir pathway, galactose fermentation and growth on galactose depend on mitochondrial function; mitochondrial dependence is elicited through the recessive allele imp1 of the nuclear gene IMP1. The genetic element IMP1 is not allelic to any of the known GAL genes; IMP1 strains can grow on and ferment galactose in respiratory-deficient (RD) condition or in the presence of the mitochondrial inhibitors ethidium bromide and erythromycin; whereas, imp1 strains can grow on and ferment galactose only in respiratory-sufficient (RS) condition. The imp1 elicited mitochondrial dependence apparently involves regulation of the synthesis of the galactose catabolizing enzymes and synthesis of the galactose specific permease. IMP1 is not the only genetic determinant that elicits an interaction of the mitochondrion and the expression of the Gal system; the GAL3 gene, whose role in galactose utilization is demonstrated by the long-term adaptation phenotype of gal3 RS mutants, gives rise to a noninducible phenotype in RD condition or in the presence of mitochondrial inhibitors.     

DNA of Akodon (Rodentia,Cricetidae). I. Biophysical characterization

Buoyant density in CsCl, melting temperature, and G + C base content of the DNA from four species of Akodon (Rodentia, Cricetidae) were determined. The buoyant density values of 1.699–1.701 g/cm³ were in accordance with the data reported for other cricetids. No satellite bands were seen in neutral CsCl. The T _m values determined in 1 × SSC ranged from 86.2 to 87.0 C, which corresponds to G + C contents of 41.2–43.2%. There was good agreement in DNA base composition of the four species, although values were slightly higher in A. obscurus, suggesting a certain degree of interspecies variability.This study was supported by grants from Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas, and Organización de Estados Americanos.     

Physical properties and Tris inhibition of an insect trehalase and a thermodynamic approach to the nature of its active site

The midgut from Rhynchosciara americana larvae display a trehalase (alpha,alpha'-trehalose glucohydrolase, EC 3.2.1.28) which is soluble with a molecular weight of 122 000 and pI 4.6. The optimum pH of the enzyme is 6.0, its apparent Km for trehalose is 0.67 mM and its energy of activation is 16.7 kcal/mol. Sulfhydryl reagents do not inhibit the trehalase. The results suggest the existence of two carboxyl groups in the active site, one of which has a very high (8.3) pK. The increase of the pK values of the essential groups of the free enzyme in the presence of increasing concentrations of dioxane supports the hypothesis that these groups are carboxyls. The purified enzyme hydrolyzes only alpha,alpha'-trehalose and it is competitively inhibited by several compounds.     

The synaptic behaviour of the X and Y chromosomes in the marsupial Monodelphis dimidiata

The pairing behaviour of the X and Y chromosomes of Monodelphis dimidiata was studied with light and electron microscopy. Pairing of the sex chromosomes is delayed with respect to autosome synapsis. Both the X and the minute Y chromosome show an axis attached by its two ends to the nuclear envelope. Synapsis of the sex chromosomes occurs by the joining of the chromatin sheaths that surround the axes and by a small, three-layered structure close to the nuclear envelope. The X and Y chromosomes remain joined to each other during the diffuse stage and diplotene-diakinesis but they do not show a synaptonemal complex. During the diffuse stage a dense plate is formed at the boundary between the X-Y body and the nuclear envelope. During early metaphase a folded sheet is attached to the periphery of the X-Y body. This sheet is formed by a piece of the nuclear envelope carrying the dense plate and it shows transverse fibrils and a central element similar to synaptonemal-complex remains. No evidence of a non-chiasmate segregation mechanism was observed. Polarization of the axial ends of the sex chromosomes is observed after X-Y synapsis. These important departures from the X-Y pairing pattern of eutherian mammals are discussed and assumed to present a special mechanism for holding the minute Y joined to the X chromosome in this marsupial.     

A diterpene acid from baccharis tucumanensis

The new clerodane diterpene 1 was isolated from the aerial parts of Baccharis tucumanensis (Compositae). Its structure has been determined from spectral data combined with chemical transformations.