Glutamine analogs promote cytoophidium assembly in human and Drosophila cells.

CTP synthase is compartmentalized within a subcellular structure, termed the cytoophidium, in a range of organisms including bacteria, yeast, fruit fly and rat. Here we show that CTP synthase is also compartmentalized into cytoophidia in human cells. Surprisingly, the occurrence of cytoophidia in human cells increases upon treatment with a glutamine analog 6-diazo-5-oxo-l-norleucine (DON), an inhibitor of glutamine-dependent enzymes including CTP synthase. Experiments in flies confirmed that DON globally promotes cytoophidium assembly. Clonal analysis via CTP synthase RNA interference in somatic cells indicates that CTP synthase expression level is critical for the formation of cytoophidia. Moreover, DON facilitates cytoophidium assembly even when CTP synthase level is low. A second glutamine analog azaserine also promotes cytoophidum formation. Our data demonstrate that glutamine analogs serve as useful tools in the study of cytoophidia.

Nitrosated peptides and polyamines as endogenous mutagens in O6-alkylguanine-DNA alkyltransferase deficient cells.

Mutants of Escherichia coli and Saccharomyces cerevisiae that lack O6-alkylguanine-DNA alkyltransferase activities have increased spontaneous mutation rates, indicating the presence of a cellular metabolite that can alkylate DNA. Bacterially catalysed nitrosation has been implicated previously in producing the endogenous alkylating agent(s). Here, nitrosated polyamines and azaserine, a model compound for nitrosated peptides, are shown to be mutagenic to E. coli ada ogt mutants deficient in O6-alkylguanine-DNA alkyltransferase activity. The mutagenicity of azaserine may be explained by its ability to methylate DNA, whereas nitrosated spermidine causes DNA damage that is susceptible to both nucleotide excision repair and O6-alkylguanine-DNA alkyltransferase activity, which indicates the generation of more bulky DNA adducts. Nitrosated peptides and polyamines are therefore potential endogenous mutagens that are harmful particularly in O6-alkylguanine-DNA alkyltransferase deficient cells.

New antitumor antibiotic, LL-D05139 beta. Fermentation, isolation, structure determination and biological activities.

The LL-D05139 complex, containing LL-D05139 beta and azaserine, was recovered from the fermentation filtrate of Glycomyces harbinensis (NRRL 15337). A chemically defined medium was developed which favored the production of LL-D05139 beta. Antibiotic LL-D05139 beta was isolated from the fermentation filtrate by adsorption on granular carbon and further purified by chromatography on microcrystalline cellulose. Acid hydrolysis of LL-D05139 beta gave one molar equivalent each of alanine and serine. Both amino acids were found to have the L-configuration by GC analysis on a chiral column and alanine was assigned to be the N-terminal amino acid by Edman degradation. This information coupled with IR, UV, 1H NMR, 13C NMR and MS spectral data allowed us to assign the structure of LL-D05139 beta as alanylazaserine. LL-D05139 beta demonstrated greater antibacterial and biochemical induction assay activities than azaserine. The two drugs showed similar antitumor activities.