Evolutionary relationships within the fungi: analyses of nuclear small subunit rRNA sequences.

Nucleotide sequences of the small subunit ribosomal RNA (18S) gene were used to investigate evolutionary relationships within the Fungi. The inferred tree topologies are in general agreement with traditional classifications in the following ways: (1) the Chytridiomycota and Zygomycota appear to be basal groups within the Fungi. (2) The Ascomycota and Basidiomycota are a derived monophyletic group. (3) Relationships within the Ascomycota are concordant with traditional orders and divide the hemi- and euascomycetes into distinct lineages. (4) The Basidiomycota is divided between the holobasidiomycetes and phragmobasidiomycetes. Conflicts with traditional classification were limited to weakly supported branches of the tree. Strongly supported relationships were robust to minor changes in alignment, method of analysis, and various weighting schemes. Weighting, either of transversions or by site, did not convincingly improve the status of poorly supported portions of the tree. The rate of variation at particular sites does not appear to be independent of lineage, suggesting that covariation of sites may be an important phenomenon in these genes.     

Proteolytic processing of chromogranin A in cultured chromaffin cells

The prohormone chromogranin A is the major soluble component of secretory granules in chromaffin cells of adrenal medulla and in many other different endocrine cell types. The proteolytic processing of chromogranin A was studied in cultured bovine chromaffin cells using [35S]methionine to label proteins and a specific antibody to immunoprecipitate the native protein and its breakdown products. In resting cells, it was found that the degradation of chromogranin A is a slow process, since no degradation was observed after a 40 h incubation with radiolabelled methionine. Stimulation of cells with a single pulse or with successive pulses of nicotine did not significantly enhance the degree of proteolytic processing of chromogranin A. As it has recently been shown (Simon, J.P., Bader, M.F. and Aunis, D. Biochem. J. (1989) 260, 915-922) that protein kinase C may be involved in the regulation of chromogranin A synthesis, the possibility that prohormone processing may also be controlled by protein kinase C was examined using the activator of protein kinase C, 12-O-tetradecanoylphorbol 13-acetate (TPA). However, incubation of cells with TPA did not significantly modify chromogranin A processing, indicating that biosynthesis and proteolytic processing of chromogranin A are two distinctly regulated mechanisms. Glucocorticoids are known to exert regulatory control of chromaffin cell metabolism; however, incubation of cells with dexamethasone did not alter slow chromogranin A processing. Stimulation of labelled cells rapidly released newly synthesized chromogranin A into external medium. In addition, released chromogranin A was found to be actively processed into its 60 kDa and 43 kDa breakdown products. This extracellular proteolytic degradation mechanism may be of importance with regard to the function of chromogranin A as a prohormone.     

Processing of precursor interleukin 1 beta and inflammatory disease

The processing of precursor interleukin 1 beta (IL1 beta) by elastase, cathepsin G, and collagenase, the major proteases released at sites of inflammation, was investigated using recombinant pro-IL1 beta. Each of these proteases cleaved the 31-kDa inactive precursor to a form similar in size and specific activity (greater than 10(8) units/mg) to the 17-kDa mature protein isolated from activated monocytes. Elastase, collagenase, and cathepsin G cleaved the IL1 beta precursor at distinct sites which are amino-terminal to the monocyte-processing site, Ala-117 (Cameron, P., Lumjuco, G., Rodkey, J., Bennett, C., and Schmidt, J. A. (1985) J. Exp. Med. 162, 790-801). Amino-terminal sequencing of the products of digestion by elastase and cathepsin G determined that resultant active IL1 beta proteins contained an additional 13 or 3 amino acids relative to mature IL1 beta. Synovial fluid collected from patients with inflammatory polyarthritis and bronchoalveolar lavage fluid from patients with sarcoidosis supplied similar processing activity(s). Control fluids from patients who had no symptoms of inflammatory disease did not exhibit processing activity. Lavage fluids that processed precursor IL1 beta were demonstrated to contain cathepsin G and/or elastase activity, whereas controls were negative. Because a significant fraction of IL1 beta may be secreted from monocytes as the inactive 31-kDa precursor (Hazuda, D. J., Lee, J. C., and Young, P. R. (1988) J. Biol. Chem. 263, 8473-8479, Bomford, R., Absull, E., Hughes-Jenkins, C., Simpkin, D., and Schmidt, J. (1987) Immunology 62, 543-549, and Mizel, S. B. (1988) in Cellular and Molecular Aspects of Inflammation Poste, G., and Crooke, S., eds) pp. 75-93, Plenum Publishing Corp., New York), these results suggest that in vivo the IL1 beta precursor can be processed after secretion by any of several proteases released at inflammatory sites.     

Depsidone constituents from the quintaria group of Nephroma species

A new lichen depsidone was isolated, in the form of its triacetate derivative from the acetylated extracts of Nephroma antarcticum and has been demonstrated to be hypoconstictic acid-triacetate. Two related depsidones, hypostictic acid hyposalazinic acid, were isolated from N. australe.     

Site-specific integration of an F'' lac pro factor in the region of the replication origin (oriC) of E. coli

Summary An episome, F 128, which carries approximately 8x10⁴ base pairs of chromosomal DNA homologous to the lac pro region of the E. coli chromosome, has been found to integrate into the oriC region of the chromosome in a site specific reaction. While the event appears to be recA-dependent, no homology between the episome and this region of the chromosome was detected. The Hfr strains formed result from the integration of intact F 128 molecules. The structure of the Hfr strains generated has been determined and their transfer properties analyzed.     

Homology between the invertible deoxyribonucleic acid sequence that controls flagellar-phase variation in Salmonella sp. and deoxyribonucleic acid sequences in other organisms.

The invertible deoxyribonucleic acid (DNA) segment cloned from Salmonella sp. was radioactively labeled and used as a probe to search for homologous sequences by Southern hybridization. Only one copy of the invertible segment could be found on the Salmonella sp. genome. Partial sequence homology with the invertible region was detected in bacteriophage Mu and P1 DNA by low-stringency hybridization. Under these conditions, no homology was detected with Escherichia coli DNA. A strain of Salmonella sp. defective in phase variation carrying the vH2- allele was also analyzed by DNA-DNA hybridization. The results show that there is sequence divergence between diphasic and vH2- strains within the invertible sequence.     

Hydrogen peroxide causes the fatal injury to human fibroblasts exposed to oxygen radicals

Oxygen radicals are suspected as being a cause of the cellular damage that occurs at sites of inflammation. The phagocytic cells that accumulate in areas of inflammation produce superoxide, hydrogen peroxide, hydroxyl radical, and probably singlet oxygen in the extracellular fluid. The mechanism by which these oxygen molecules kill cells is unknown. To determine which of the oxygen species is responsible for the cellular killing, we exposed human fibroblasts in culture to oxygen radicals generated by the enzymatic action of xanthine oxidase upon acetaldehyde. Using the amount of chromium-51 released from labeled fibroblasts as an index of cellular death, we found that cells were protected only by interventions that reduce hydrogen peroxide concentration. Agents that inactivate superoxide, hydroxyl radical, and singlet oxygen were ineffective in limiting oxygen radical-induced cellular death.