The p53 isoforms are differentially modified by Mdm2

The discovery that the single p53 gene encodes several different p53 protein isoforms has initiated a flurry of research into the function and regulation of these novel p53 proteins. Full-length p53 protein level is primarily regulated by the E3-ligase Mdm2, which promotes p53 ubiquitination and degradation. Here, we report that all of the novel p53 isoforms are ubiquitinated and degraded to varying degrees in an Mdm2-dependent and -independent manner, and that high-risk human papillomavirus can degrade some but not all of the novel isoforms, demonstrating that full-length p53 and the p53 isoforms are differentially regulated. In addition, we provide the first evidence that Mdm2 promotes the NEDDylation of p53β. Altogether, our data indicates that Mdm2 can distinguish between the p53 isoforms and modify them differently.     

Selection of strains of Streptomyces griseus Kr., the producer of a streptothricin antibiotic grisin, using the method of protoplast fusion

The effect of protoplasting on antibiotic activity of the grisin-producing organism was shown. High frequency of Grn- mutants after strain VG307f protoplasting and no capacity in these mutants for reversion to the initial Grn+ phenotype were shown. The reversion frequency was less than 10(-8). Moreover, it was shown that all the Grn- mutants lost their stability (GrnR) to the effect of their own antibiotic. With respect to strain VG212 there was noted a significant increase in the number of both the minus and the plus variants after the protoplast formation and regeneration. Fusing of protoplasts of strains VG307f and VG212 belonging to the divergent lines in selection of S. griseus Kr. yielded the phage stable strain VG7849 with high levels of the antibiotic production and improved technological properties.     

Identification of Glycolytic Enzyme Polypeptides on the Two-Dimensional Protein Map of Saccharomyces cerevisiae and Application to the Study of Some Wine Yeasts

Using a modification of the basic two-dimensional polyacrylamide gel electrophoresis technique, the polypeptides of the protein map of Saccharomyces cerevisiae involved in glycolysis were investigated. This study resulted in a reassignment of two of the seven glycolytic enzyme polypeptides previously identified (Ludwig et al., Mol. Cell. Biol. 2:117-126, 1982), those corresponding to phosphoglycerate kinase and to alcohol dehydrogenase. It also resulted in the identification of two additional glycolytic polypeptides, the enolase B monomer and the glyceraldehyde phosphate dehydrogenase B monomer. The glycolytic enzymes polypeptides so identified were investigated in 5 laboratory strains (all S. cerevisiae) and in 11 commerical strains used for wine making (S. cerevisiae and Saccharomyces bayanus). It appeared highly significant that a particular electrophoretic variant of the glyceraldehyde phosphate dehydrogenase B monomer was found only in the wine yeasts. Furthermore, it was strongly suggested that S. cerevisiae and S. bayanus strains are distinguishible on the basis of a different electrophoretic migration of the enolase B monomer.     

Coexistence of incompatible plasmids in a bacterial population living under a feast and famine regime

A model is formulated to examine the possibility of (co)existence of plasmids of the same incompatibility and surface exclusion group in a bacterial population living under a feast-and-famine regime. The condition is given under which a growth rate decreasing plasmid can invade a bacterial population. It appears that in case only one plasmid type is present, the frequency of plasmid bearers will tend to a stable equilibrium if the food supply at each growth site gets exhausted and if both plasmid-free and plasmid-bearing bacteria need an equal quantity of food per cell division. If these two conditions are not satisfied, the frequency of plasmid-bearers might oscillate. Two plasmids will sometimes be able to coexist, but only if they follow different survival strategies; one with a high conjugational transfer rate and a lower fitness of its host, and the other with a low transfer rate and a higher host fitness. Coexistence of three plasmids of the same surface exclusion group is impossible.     

A technique for maintaining explants in contact with solid medium in petri dishes

Summary The objective of this study was to develop a system to maintain orchardgrass (Dactylis glomerata L.) leaf segments in contact with solid medium in petri dishes during different orientation of the dishes. To ensure contact with the medium, leaf segments were overlaid with 1800 m Teflon mesh. This was secured with a polypropylene ring which fitted between the petri dish lid and the mesh. This procedure did not affect the somatic embryogenesis response. A significant difference (P=0.05) in increased ethylene accumulation from overlaid segments was recorded on day 5.     

Three-dimensional 1H NMR structure of the nucleocapsid protein NCp10 of Moloney murine leukemia virus

Summary The nucleocapsid protein of Moloney murine leukemia virus (NCp10) is a 56-amino acid protein which contains one zinc finger of the CysX₂CysX₄HisX₄Cys form, a highly conserved motif present in most retroviruses and retroelements. At pH5, NCp10 binds one zinc atom and the complexation induces a folding of the CysX₂CysX₄HisX₄Cys box, similar to that observed for the zinc-binding domains of HIV-1 NC protein. The three-dimensional structure of NCp10 has been determined in aqueous solution by 600 MHz ¹H NMR spectroscopy. The proton resonances could be almost completely assigned by means of phase-sensitive double-quantum-filtered COSY, TOCSY and NOESY techniques. NOESY spectra yielded 597 relevant structural constraints, which were used as input for distance geometry calculations with DIANA. Further refinement was performed by minimization with the program AMBER, which was modified by introducing a zinc force field. The solution structure is characterized by a well-defined central zinc finger (rmsd of 0.747±0.209 Å for backbone atoms and 1.709±0.187 Å when all atoms are considered), surrounded by flexible N- and C-terminal domains. The Tyr²⁸, Trp³⁵, Lys³⁷, Lys⁴¹ and Lys⁴² residues, which are essential for activity, lie on the same face of the zinc finger, forming a bulge structure probably involved in viral RNA binding. The significance of these structural characteristics for the various biological functions of the protein is discussed, taking into account the results obtained with various mutants.