Evidence for H-2-linked control of retrovirus production in Friend virus-induced tumor cell lines.

In Friend leukemia virus-induced tumor cell lines derived from mice congenic with respect to the H-2 complex, most cell lines expressing the H-2k haplotype continuously produced infectious exogenous virus in culture, whereas most cell lines expressing the H-2b or H-2d haplotype stopped producing virus during in vitro passage. This apparent H-2-linked control of virus production did not appear to be the result of alteration of the provirus or resistance to superinfection. The implications of this finding with respect to virus-induced leukemogenesis are discussed.     

Ammonium repression of cephalosporin production by Streptomyces clavuligerus

Production of beta-lactam antibiotics took place during growth of Streptomyces clavulgerus in chemically defined medium. The specific activities of isopenicillin N synthetase ("cyclase"), isopenicillin N epimerase, and deacetoxycephalosporin C synthetase ("expandase") increased during the exponential phase of growth. Specific cephalosporin productivity during fermentation followed a similar pattern, reaching a maximum near the end of the growth phase and decaying rapidly in the stationary phase. Ammonium chloride depressed cephalosporin production, presumably as a result of repression of cyclase and expandase formation, but not of epimerase. No inhibitory effects on enzyme activity by ammonium were found. Addition of tribasic magnesium phosphate [Mg3(PO4)2 X 8H2O] prevented the repression of cyclase and markedly stimulated cephalosporin production. Cephamycin C and, in smaller amounts, O-carbamoyldeacetylcephalosporin C were the only cephalosporins detected. Growth with ammonium resulted in lower titers of both compounds, and did not change the relative proportion of each. The correlation found between cephalosporin productivity and cyclase specific activity in different media suggests that formation of this enzyme may be the rate-limiting step in the pathway.     

Isolation and characterization of an alphoid centromeric repeat family from the human Y chromosome

A collection of human Y-derived cosmid clones was screened with a plasmid insert containing a member of the human X chromosome alphoid repeat family, DXZ1. Two positive cosmids were isolated and the repeats they contained were investigated by Southern blotting, in situ hybridization and sequence analysis. On hybridization to human genomic DNAs, the expected cross-hybridization characteristic of all alphoid sequences was seen and, in addition, a 5500 base EcoRI fragment was found to be characteristic of a Y-specific alphoid repeat. Dosage experiments demonstrated that there are about 100 copies of this 5500 base EcoRI alphoid fragment on the Y chromosome. Studies utilizing DNA from human-mouse hybrids containing only portions of the Y chromosome and in situ hybridizations to chromosome spreads demonstrated the Y centromeric localization of the 5500 base repeat. Cross-hybridization to autosomes 13, 14 and 15 was also seen; however, these chromosomes lacked detectable copies of the 5500 base EcoRI repeat sequence arrangement. Sequence analysis of portions of the Y repeat and portions of the DXZ1 repeat demonstrated about 70% homology to each other and of each to the human consensus alphoid sequence. The 5500 base EcoRI fragment was not seen in gorilla, orangutan or chimpanzee male DNA.     

Chronic exercise and left ventricular structure and function in healthy human subjects

Twelve healthy well-trained participants in a supervised exercise program (mean age, 41.3 yr) were compared with 12 sedentary control subjects (mean age, 38.9 yr) with physical characteristics similar to the exercised group (EG) before training. Resting echocardiograms revealed significantly lower heart rates (HR) in the EG compared with control group (CG) but no evidence for cardiac structural differences between groups. Radionuclide angiograms performed at rest and during two levels of supine cycling (HR targets: 120 and 140 beats X min-1) resulted in increases in background-corrected end-diastolic counts [EDC(bc)] and confirmed use of the Frank-Starling mechanism in the majority of subjects. Mean values (+/- SD) for ejection fraction (EF) and normalized peak systolic ejection rate (PSER) (P greater than 0.05 between groups) were the following. (Formula: see text) The results suggested that fitness training does not induce significant cardiac enlargement as apparent from measurements at rest or important changes in contractile state during exercise. Increases in exercise stroke volume with such training may be the result of an increased end-diastolic volume.     

Multidirectional differentiation in neuroendocrine neoplasms

Histopathological and experimental observations indicate that tumors composed wholly or in part of neuroendocrine elements may arise in tissues derived from ectoderm (including neuroectoderm), mesoderm, and endoderm. These tumors frequently exhibit multidirectional differentiation as manifested by multihormonality and by the presence of morphological features indicative of divergent differentiation both in vivo and in vitro. The existence of stem cells, plasticity of differentiated cells, microenvironmental influences, and random events are factors which might all interact to determine the characteristics of any particular tumor. The production of characteristic regulatory peptide products in association with tumors of specific histological subtypes and with other neuroendocrine markers suggests mechanisms for nonrandom activation of multiple genes common to neuroendocrine-programmed cells. Future studies applying new molecular biological techniques to intact tissues and to in vitro models may help to clarify the mechanisms that regulate the expression of the neuroendocrine phenotype in normal and neoplastic states.     

Association between cutaneous occlusive vascular disease, cigarette smoking, and skin slough after rhytidectomy

This prospective study attempted to determine if nonreversible occlusive vascular changes in the skin contribute to skin slough after rhytidectomy. The dermal microvasculature from 83 consecutive rhytidectomies was evaluated for intimal proliferation and/or hyalin sclerosis. Occlusive vascular disease increased progressively with age in all patients, but smokers and ex-smokers had significantly greater involvement than nonsmokers at any given age (p = 0.03). Severe occlusive vascular disease and skin slough were associated (p = 0.02), and there was a strong trend toward an association between active smoking and skin slough (p = 0.06). Among smokers, there was a significant relationship between skin slough and failure to abstain from smoking postoperatively (p = 0.006). We conclude that with aging, nonreversible occlusive changes develop in the dermal microvasculature. These changes appear to be accelerated by cigarette smoking. Our data, however, show that these nonreversible occlusive vascular changes by themselves do not completely account for the occurrence of skin slough after rhytidectomy.     

Effects of embryo-freezing and thawing techniques on the survivability of Brucella abortus

A suspension of a pathogenic strain (2308) of Brucella abortus was aliquoted, centrifuged, resuspended in 6 treatment media and quantitated. Ten 1-ml samples of each treatment were subjected to a standard embryo-freezing technique. The treatments were selected to examine the effects of 1) freezing and thawing, 2) cryoprotectants and 3) antibiotics on the survivability of Brucella suspended in embryo-support media. Five samples of each treatment were thawed and quantitated after a 2-wk storage period and five samples were thawed and quantitated after a 6-mo storage period. Means and percent reductions were determined for each treatment. There was no statistical difference between means at 2 wk and 6 mo within any treatment. Freezing and thawing caused a 64% reduction in the number of viable Brucella . The addition of antibiotics caused a 99.9% reduction in viability of the organism. Glycerol protected the organism during freezing and thawing in the absence of antibiotics but did not interfere with the high percent reduction seen when antibiotics were present. Dimethylsulfoxide (DMSO), however, not only protected the organism during freezing and thawing but also appeared to negate the effects of the antibiotics.     

Isopenicillin N epimerase activity in a high cephalosporin-producing strain of Cephalosporium acremonium

Summary Isopenicillin N epimerase activity in Cephalosporium acremonium CW-19 is so labile that it has never been detected in sonic extracts. Prior to this work, it had only been obtained by the laborious protoplast lysate procedure. The present work shows that the enzyme is present in sonic extracts of a high cephalosporin-producing strain (C-10) of C. acremonium throughout the fermentation.     

Activation of the methylreductase system from Methanobacterium bryantii by ATP.

The methylreductase of Methanobacterium bryantii required ATP for activity. There was sufficient ATP synthesis in extracts to account for the observed activity. Hexokinase inhibited the methylreductase by competing for endogenously synthesized ATP. The uncoupler, carbonyl cyanide p-trifluoromethyoxyphenyl hydrazone, inhibited only at concentrations greater than 0.5 mM, and detergents and non-halogenated membrane-permeable-ions did not inhibit. Thus, membrane proton gradients are not important in activation. In addition, maximal activation was obtained with less than 0.25 mM ATP, was inhibited by beta, gamma-imido ATP, and was strongly temperature dependent. The activated state was very unstable, having a half-life of 5 to 15 min. After gel filtration at 5 degrees C, the methylreductase retained partial activity for a short time in the absence of ATP. These observations indicate that activation involves the modification of a protein or protein-bound cofactor of the methylreductase system.