Degradation of HeLa S3 cell chromatin by auromomycin and its chromophore

The antitumor protein agent auromomycin was found to degrade chromatin structure primarily by inducing strand scissions in linker regions. The reaction was stimulated by dithiothreitol. The chromophore form of the drug caused similar effects on chromatin, but it appeared to function at a more rapid rate. There was no evidence that auromomycin could cause breakage in core regions of chromatin.     

Degradation of Microtubule-Associated Protein 2 and Brain Spectrin by Calpain: A Comparative Study

The in vitro degradation of microtubule-associated protein 2 (MAP-2) and spectrin by the calcium-dependent neutral protease calpain was studied. Five major results are reported. First, MAP-2 isolated from twice-cycled microtubules (2 X MT MAP-2) was extremely sensitive to calpain-induced hydrolysis. Even at an enzyme-to-substrate ratio (wt/wt) of 1:200, 2 X MT MAP-2 was significantly degraded by calpain. Second, MAP-2 purified from the total brain heat-stable fraction (total MAP-2) was significantly more resistant to calpain-induced hydrolysis compared with 2 X MT MAP-2. Third, MAP-2a and MAP-2b were proteolyzed similarly by calpain, although some relative resistance of MAP-2b was observed. Fourth, the presence of calmodulin significantly increased the extent of calpain-induced hydrolysis of the alpha-subunit of spectrin. Fifth, the two neuronal isoforms of brain spectrin (240/235 and 240/235E, referred to as alpha/beta N and alpha/beta E, respectively) showed different sensitivities to calpain. alpha N-spectrin was significantly more sensitive to calpain-induced degradation compared to alpha E-spectrin. Among other things, these results suggest a role for the calpain-induced degradation of MAP-2, as well as spectrin, in such physiological processes as alterations in synaptic efficacy, dendritic remodeling, and in pathological processes associated with neurodegeneration.     

Mouse X chromosome

Overall, the probe map fromDXWas70 toAmg encompasses 72 cM and includes 103 loci. Eight of these have been designated reference loci (see Table 2 and previous section) on account of their wide usage that would enable the cross reference of independent maps created in different laboratories. Reference loci are to be readily available and easily used probes for Southern hybridization. By and large, they will be STSs, regeneratable by PCR, and correspond to a known gene. In addition, on the mouse X Chr, there is a reference locus from each of the known conserved linkage groups found between the mouse and human X Chrs. All the loci, barDXWas31, represent conserved sequences. Committee Members: D. Adler, P.J. Barnard, Y. Boyd, N. Brockdorff, J. Derry, C. Disteche, C. Faust, M.F. Lyon, S. Rastan, M. Seldin and L. Siracusa.     

Ecosystem health as measured from the molecular to the community level of organization,with reference to sediment bioassessment

The current recognition that chemical measurements are uncertain indicators of biological consequences of pollution has shifted the emphasis away from assessing environmental chemistry alone toward the inclusion of measurements of the health of organisms. Effects of pollutants begin with the individual, have subsequent repercussions on population level processes, and ramifications for community structure and functions. Pollutants act at a molecular level and the biochemical lesions is the first step in the manifestation of effects. Technologies that operate at the cellular level assist in elucidating toxicity. Higher levels of integration include an organism's capacity for growth. Laboratory bioassays andin situ research can monitor physiological incapacities and assist in predicting population level effects. A yet higher level of organization is that of the ecological community.     

Inhibition of cyclic amp phosphodiesterase by 5'-deoxy-5'-S-isobutylthioadenosine at biologically active concentrations of drug

5'-Deoxy-5'-S-isobutylthioadenosine (SIBA), a synthetic analogue of S-adenosylhomocysteine, has been reported by others to inhibit a number of biological processes and these effects of SIBA have been attributed generally to inhibition of methyltransferases. However, the present studies with mouse lymphocytes show that SIBA also acts as a competitive inhibitor (K_i = 130 μM) of the high-affinity cyclic AMP phosphodiesterase and potentiates the cyclic AMP response of intact cells to several activators of adenylate cyclase. Moreover, SIBA has been found to inhibit lymphocyte-mediated cytolysis, a cellular function known to be sensitive to elevated lymphocyte levels of cyclic AMP, at concentrations (IC₅₀ = 250 μM) similar to those which inhibit cyclic AMP phosphodiesterase. These results indicate the need for caution in attributing biological effects of SIBA singularly to inhibition of methyltransferases and suggest the possible agency of cyclic AMP in the mechanism of SIBA action.     

Pi Ecincinnati: A new alpha1-antitrypsin allele in three negro families

Summary Serum specimens of three unrelated black males had an unusual alpha-1-antitrypsin phenotype, designated Pi Ecincinnati because of its electrophoretic mobility. Family studies indicated that the new phenotype was the expression of an alpha-1-antitrypsin allele, labeled Pi ^Ecincinnati     

Outer Membrane-Dependent Transport Systems in Escherichia coli: Effect of Repression or Cessation of Colicin Receptor Synthesis on Colicin Receptor Activities

Proteins in the outer membrane of gram-negative bacteria serve as general porins or as receptors for specific nutrient transport systems. Many of these proteins are also used as receptors initiating the processes of colicin or phage binding and uptake. The functional activities of several outer membrane proteins in Escherichia coli K-12 were followed after cessation or repression of their synthesis. Cessation of receptor synthesis was accomplished with a thermolabile suppressor activity acting on amber mutations in btuB (encoding the receptor for vitamin B(12), the E colicins, and phage BF23) and in fepA (encoding the receptor for ferric enterochelin and colicins B and D). After cessation of receptor synthesis, cells rapidly became insensitive to the colicins using that receptor. Treatment with spectinomycin or rifampin blocked appearance of insensitive cells and even increased susceptibility to colicin E1. Insensitivity to phage BF23 appeared only after a lag of about one division time, and the receptors remained functional for B(12) uptake throughout. Therefore, possession of receptor is insufficient for colicin sensitivity, and some interaction of receptor with subsequent uptake components is indicated. Another example of physiological alteration of colicin sensitivity is the protection against many of the tonB-dependent colicins afforded by provision of iron-supplying siderophores. The rate of acquisition of this nonspecific protection was found to be consistent with the repression of receptor synthesis, rather than through direct and immediate effects on the tonB product or other components of colicin uptake or action.     

Activation of human B lymphocytes: XVI. Cellular requirements,interactions, and immunoregulation of pokeweed mitogen-induced total-immunoglobulin producing plaque-forming cells in peripheral blood

The optimal culture and assay conditions for the detection of spontaneously occurring and pokeweed mitogen (PWM)-induced polyvalent Ig (IgG + IgM + IgA) and individual Ig class-specific plaque-forming cells (PFC) in human peripheral blood have been described in detail. Culture conditions are critical, particularly with regard to cell density and batches of supplemental serum. Fetal calf serum is a much more supportive serum supplement for PWM-induced PFC than is human serum. The assay system is a modified reverse hemolytic PFC assay using staphylococcal protein A coupled to sheep red blood cells by the chromic chloride method. PFC are developed by rabbit anti-human polyvalent Ig or anti-human individual Ig class antisera. Human peripheral blood contains 468 (±78) spontaneously occurring Ig secreting PFC per 10⁶ lymphocytes at Day 0 and 20,500(± 1971) PWM-induced Ig secreting PFC after 6 days in culture. The response is T-cell dependent; however, T cells can be replaced by a soluble T-cell factor prepared from a 48-hr allogeneic mixed lymphocyte reaction supernatant. The relative dependence on monocytes is a reflection of the culture conditions employed. Under the conditions of round-bottom tubes which promote cell-to-cell contact, depletion of monocytes to 0 to 2% does not result in a diminution of PFC responses. In fact, under such conditions, in certain individuals monocytes are markedly suppressive such that removal of monocytes results in a substantial enhancement of PFC responses. This system is simple and reproducible and should prove extremely useful in the delineation of the mechanisms of B-cell triggering and immunoregulation in normals and in disease states.