Kinetics of beta-tubulin exchange following translation. Evidence for a slow conformational change in beta-tubulin necessary for incorporation into heterodimers

Cell-free translation of beta-tubulin mRNA generates full length beta-tubulin polypeptides distributed in three molecular forms: a high molecular weight lysate-associated form, the free beta-tubulin subunit, and the alpha beta-heterodimer (Yaffe, M.B., Farr, G. W., and Sternlicht, H. (1988) J. Biol. Chem. 263, 16023-16031). A quantitative assay system for these three forms was developed and used to measure the rates of incorporation/exchange of the newly synthesized free beta-subunit and the high molecular weight form into tubulin heterodimers following incubation of the 35S-translation products with unlabeled bovine tubulin dimer. This exchange process was found to be slow and strongly temperature-dependent. The half-lives for exchange ranged from 12.5 min at 37 degrees C to 17.5 h at 0 degree C with a measured activation energy of 22.5 kcal/mol. Microtubule-associated proteins appeared to play no role in the exchange process, since identical exchange rates were observed regardless of whether microtubule protein or phosphocellulose-purified tubulin was used as the source of tubulin dimer. Surprisingly, the exchange rates were found to be independent of dimer concentration. We interpret these results as evidence for a rate-limiting, slow conformational change that occurs within the newly synthesized beta-subunits prior to their association with alpha-tubulin to generate the alpha beta-hetero-dimer.     

Orientation of dioxygen bound to cobalt(II) bleomycin-DNA fibers

The molecular oxygen adduct of Co(II)-bleomycin is stable for long periods when bound to salmon sperm DNA at large ratios of polymer to drug. According to ESR studies of orientation of the paramagnetic complex associated with DNA fibers, the oxygen-oxygen bond is restricted to a plane perpendicular to the fiber axis. Thus, one can define three g values for the adduct 2.104, 2.016, and 2.000, one parallel to the fiber axis and two orthogonal to it. There is no change in orientation over the range of 77 K to ambient temperature. Furthermore, there is no difference in results at a series of relative humidities ranging from less than 76% where bulk DNA alone assumes an A conformation to 95% where it is primarily B DNA. A structural model is presented for the geometry of the metal binding domain of O2-Co-bleomycin in relationship to the fiber axis of DNA.     

Screening of significant biomarkers related with prognosis of liver cancer by lncRNA-associated ceRNAs analysis

This study aimed to identify significant biomarkers related to the prognosis of liver cancer using long noncoding RNA (lncRNA)-associated competing endogenous RNAs (ceRNAs) analysis. Differentially expressed mRNA and lncRNAs between liver cancer and paracancerous tissues were screened, and the functions of these mRNAs were predicted by gene ontology and pathway enrichment analyses. A ceRNA network consisting of differentially expressed mRNAs and lncRNAs was constructed. LncRNA FENDRR and lncRNA HAND2-AS1 were hub nodes in the ceRNA network. A risk score assessment model consisting of eight genes (PDE2A, ESR1, FBLN5, ALDH8A1, AKR1D1, EHHADH, ADRA1A, and GNE) associated with prognosis were developed. Multivariate Cox regression suggested that both pathologic_T and risk group could be regarded as independent prognostic factors. Furthermore, a nomogram model consisting of pathologic_T and risk group showed a good prediction ability for predicting the survival rate of liver cancer patients. The nomogram model consisting of pathologic_T and a risk score assessment model could be regarded as an independent factor for predicting prognosis of liver cancer.     

Rapid Transepithelial Transport of Prions following Inhalation

Prion infection and pathogenesis are dependent on the agent crossing an epithelial barrier to gain access to the recipient nervous system. Several routes of infection have been identified, but the mechanism(s) and timing of in vivo prion transport across an epithelium have not been determined. The hamster model of nasal cavity infection was used to determine the temporal and spatial parameters of prion-infected brain homogenate uptake following inhalation and to test the hypothesis that prions cross the nasal mucosa via M cells. A small drop of infected or uninfected brain homogenate was placed below each nostril, where it was immediately inhaled into the nasal cavity. Regularly spaced tissue sections through the entire extent of the nasal cavity were processed immunohistochemically to identify brain homogenate and the disease-associated isoform of the prion protein (PrP^d). Infected or uninfected brain homogenate was identified adhering to M cells, passing between cells of the nasal mucosa, and within lymphatic vessels of the nasal cavity at all time points examined. PrP^d was identified within a limited number of M cells 15 to 180 min following inoculation, but not in the adjacent nasal mucosa-associated lymphoid tissue (NALT). While these results support M cell transport of prions, larger amounts of infected brain homogenate were transported paracellularly across the respiratory, olfactory, and follicle-associated epithelia of the nasal cavity. These results indicate that prions can immediately cross the nasal mucosa via multiple routes and quickly enter lymphatics, where they can spread systemically via lymph draining the nasal cavity.