Kettering University

About: Kettering University is a education organization based out in Flint, Michigan, United States. It is known for research contribution in the topics: RNA & Antigen. The organization has 6842 authors who have published 7689 publications receiving 337503 citations. The organization is also known as: GMI Engineering & Management Institute & General Motors Institute.

The toxic effects of 6-mercaptopurine and related compounds

Abstract: The present review of the toxic effects of 6-mercaptopurine (6-MP) in experimental mammals has two primary aims. The first and more practical purpose concerns risks to be anticipated during therapeutic use. The second aim concerns the specific cytocidal effects of 6-MP as a possible contribution to the elucidation of its mechanism of action. As such, the study is a continuation of work of this laboratory by which i t has been possible to differentiate the cytotoxic effects of folic acid antagonists such as aminopterinl and certain diaminopyrimidines2s2a from those of the nitrogen mustards and mustardlike compounds, such as HN2 and TEM; and from those of 2,6-diaminopuIn the present instance, tissue changes induced by 6-MP are compared with those caused by 2,6-diaminopurine (2,6-DAP) and by other purine analogs. Certainly if the action of 6-MP is to be explained in terms of a specific metabolite antagonism, then such an exposition must draw sustenance not only from differences in toxic properties between 6-MP and, for example, 2,6-DAP1 but must also reconcile similarities in the effects of these compounds. Toxicity studies. FIGURE 1 provides a list of the purines employed and presents graphically their relative potency in terms of toxicity in Swiss male mice. In most instances, two schedules of dosage have been used, i.e., single and five successive daily injections. The agents are listed in an order largely based on their relative potency by chronic administration. The bars topped by arrows refer to the fact that the highest dose employed, the quantity indicated by the height of the serrated column, is less than LDso. Data are taken from previous reports45 , 6. and from unpublished observations of the author^.^ The graph illustrates that there is more than a hundredfold difference in potency between the two extreme members of the series. Moreover, 6-MP is neither the most nor least toxic of its close structural analogs. The extent by which the toxicity of each compound is enhanced by cumulative action can be appreciated by comparing the LDE0 of single doses with that of multiple doses. It may be seen that most of the compounds, including 6-MP, exhibit relatively minor cumulative activity, i.e., the LDso in mgm./kg./day for five daily doses, when expressed as a fraction of the single median lethal dose, ranges between one fourth in the case of adenine to more than one half in the case of 6-chloro-

On the remarkable antitumor properties of fludelone: how we got there.

Abstract: Small-molecule natural products are presumably often biosynthesized with a view to optimizing their ability to bind to strategic proteins or other biomolecular targets. Although the ultimate setting in which a drug must function may be very different, the use of such natural products as lead compounds can serve as a significant head start in the hunt for new agents of clinical value. Herein we reveal the synergistic relationship between chemical synthesis and drug optimization in the context of our research program around the epothilones: how synthesis led to the discovery of more-potent epothilone derivatives, and discovery inspired the development of new synthetic routes, thus demonstrating the value of target-directed total synthesis in the quest for new substances of material clinical benefit.

Accelerated mRNA decay in conditional mutants of yeast mRNA capping enzyme

Abstract: Current models of mRNA decay in yeast posit that 3' deadenylation precedes enzymatic removal of the 5' cap, which then exposes the naked end to 5' exonuclease action. Here, we analyzed gene expression in Saccharomyces cerevisiae cells bearing conditional mutations of Ceg1 (capping enzyme), a 52 kDa protein that transfers GMP from GTP to the 5' end of mRNA to form the GpppN cap structure. Shift of ceg1 mutants to restrictive temperature elicited a rapid decline in the rate of protein synthesis, which correlated with a sharp reduction in the steady-state levels of multiple individual mRNAs. ceg1 mutations prevented the accumulation of SSA1 and SSA4 mRNAs that were newly synthesized at the restrictive temperature. Uncapped poly(A)+ SSA4 mRNA accumulated in cells lacking the 5' exoribonuclease Xrn1. These findings provide genetic evidence for the long-held idea that the cap guanylate is critical for mRNA stability. The deadenylation-decapping-degradation pathway appears to be short-circuited when Ceg1 is inactivated.

Activator control of nucleosome occupancy in activation and repression of transcription.

Abstract: The relationship between chromatin structure and gene expression is a subject of intense study. The universal transcriptional activator Gal4 removes promoter nucleosomes as it triggers transcription, but how it does so has remained obscure. The reverse process, repression of transcription, has often been correlated with the presence of nucleosomes. But it is not known whether nucleosomes are required for that effect. A new quantitative assay describes, for any given location, the fraction of DNA molecules in the population that bears a nucleosome at any given instant. This allows us to follow the time courses of nucleosome removal and reformation, in wild-type and mutant cells, upon activation (by galactose) and repression (by glucose) of the GAL genes of yeast. We show that upon being freed of its inhibitor Gal80 by the action of galactose, Gal4 quickly recruits SWI/SNF to the genes, and that nucleosome “remodeler” rapidly removes promoter nucleosomes. In the absence of SWI/SNF, Gal4′s action also results in nucleosome removal and the activation of transcription, but both processes are significantly delayed. Addition of glucose to cells growing in galactose represses transcription. But if galactose remains present, Gal4 continues to work, recruiting SWI/SNF and maintaining the promoter nucleosome-free despite it being repressed. This requirement for galactose is obviated in a mutant in which Gal4 works constitutively. These results show how an activator's recruiting function can control chromatin structure both during gene activation and repression. Thus, both under activating and repressing conditions, the activator can recruit an enzymatic machine that removes promoter nucleosomes. Our results show that whereas promoter nucleosome removal invariably accompanies activation, reformation of nucleosomes is not required for repression. The finding that there are two routes to nucleosome removal and activation of transcription—one that requires the action of SWI/SNF recruited by the activator, and a slower one that does not—clarifies our understanding of the early events of gene activation, and in particular corrects earlier reports that SWI/SNF plays no role in GAL gene induction. Our finding that chromatin structure is irrelevant for repression as studied here—that is, repression sets in as efficiently whether or not promoter nucleosomes are allowed to reform—contradicts the widely held, but little tested, idea that nucleosomes are required for repression. These findings were made possible by our nucleosome occupancy assay. The assay, we believe, will prove useful in studying other outstanding issues in the field.