Ultraviolet Mutagenesis and Its Repair in an ESCHERICHIA COLI Strain Containing a Nonsense Codon

Ultraviolet mutagenesis and its repair were studied mainly in WU36-10-89, a uvr(-) strain of Escherichia coli containing a UAG mutation in a gene for leucine biosynthesis. Following ultraviolet (UV) irradiation revertants appearing with or without direct photoreactivation (PR) were classified according to the presence and type of suppressor they contained. We find UV mutation production to be quite specific. An analysis of revertants produced by UV indicates they are formed mainly from GC --> AT and that the miscoding is due to a cytosine residue at the site of mutation in a cytosine-thymine (CT) dimer. We propose that the dimer serves as template during some aspects of repair replication and at the time of replication the C in the dimer directs the insertion of A in the complementary strand. We also note that C --> A and T -->G changes caused by a CT dimer occur much less frequently.     

Do urinary mononuclear cells reflect disease activity in lupus nephritis?

Glomerular inflammation is associated with urinary mononuclear cells (UMC) in a number of diseases including IgA nephropathy and glomerulonephritis. We examined UMC from children with lupus nephritis for a number of years to characterize the types of mononuclear cells found in urine and to determine if they were associated with active lupus nephritis. Detailed analysis of UMC by cell counts and by flow cytometry showed that monocytes were the clearly dominant cell type. Evaluation of the smaller number of lymphocytes found in the urine of patients with active lupus nephritis demonstrated a strong predominance of CD8+ lymphocytes, in contrast to the normal CD4+/CD8+ ratio that is found in peripheral blood. The degree of proteinuria strongly correlated with the presence of UMC. The UMC counts decreased as their clinical condition improved as indicated by lower indices of flare. These observations suggest that UMC may be a valuable tool in detecting and monitoring disease activity in patients with severe lupus nephritis. More importantly, this study indicated that both monocytes and cytotoxic CD8+ T cells may play a role in pathogenesis of lupus nephritis.     

Alterations of Neutral Glycolipids in Cells Infected with Syncytium-Producing Mutants of Herpes Simplex Virus Type 1

The isolation of syncytium-producing mutants of herpes simplex virus type 1 (KOS strain), which cause extensive cell fusion during otherwise normal infections, has been reported previously (S. Person, R. W. Knowles, G. S. Read, S. C. Warner, and V. C. Bond, J. Virol. 17:183-190, 1976). Seven of these mutants, plus two syncytial strains obtained elsewhere, were used to compare the incorporation of labeled galactose into neutral glycolipids of mock-infected, wild-type-infected, and syncytially infected human embryonic lung cells. Five predominant cellular glycolipid species were observed, denoted GL-1 through GL-5 in order of increasing oligosaccharide chain length; for example, GL-1 and GL-2 correspond to glycolipids that contain mono- and disaccharide units, respectively. Wild-type virus infection caused an increase in galactose incorporation into GL-1 and GL-2 relative to GL-3 through GL-5. For a single labeling interval from 4 to 10 h after adsorption, syncytial infections generally resulted in a relatively greater incorporation into more complex glycolipids than did wild-type infections. One mutant, syn 20, was compared with wild-type virus throughout infection by using a series of shorter labeling pulses and appeared to delay by at least 2 h the alterations observed during wild-type infections. These alterations are apparently due to defects in synthesis, since prelabeled cellular glycolipids were not differentially degraded during mock or virus infection.     

Investigation of the silent period by a poststimulus histogram method

The silent period after isotonic contraction induced by nerve stimulation was investigated in the human hand muscles. By using a method of poststimulus histograms of motor unit potentials and stimuli of submaximal strength for the M-response, after-hyperpolarization of the motoneurons could be excluded from the experiments. The silent period under these conditions appeared not earlier than 60 msec after stimulation; in its parameters it was similar to the silent period observed after stimulation of the nerve at subthreshold strengths for the M-response or stimulation of the skin. The experimental results thus showed that spinal effects of recurrent inhibition and spindle unloading to not occur in the hand muscles. The degree to which autogenous inhibition participates in the silent period is still uncertain. It is concluded that the role of negative feedback closed at the spinal level in the regulation of muscular contraction is not as important as has hitherto been considered on the basis of the study of the silent period.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 177–185, March–April, 1978.     

Effects of substrate biodegradability on the mass and activity of the associated estuarine microbiota

Multiple biochemical assays of microbial mass and activities were applied to the estuarine detrital microbiota colonizing morphologically similar polyvinyl chloride needles and needles from slash pine (Pinus elliottii). Biodegradable pine needles consistently showed 2- to 10-fold higher values of extractable adenosine 5'-triphosphate, rates of oxygen utilization, activities of alkaline phosphatase and phosphodiesterase, and the mucopeptide cell wall component muramic acid than did the polyvinyl chloride needles, during a 14-week incubation in a semitropical estuary. The higher activities by the microbiota of the biodegradable substrate correlated with estimates of the microbial density from scanning electron microscopy. The microbial community associated with the nondegradable substrate showed minimal activity of beta-d-galactosidase, beta-d-glucosidase, and alpha-d-mannosidase in contrast to the biota of the degradable substrate, which showed 10- to 100-fold higher activities of these glycoesterases. These enzymes logically could be involved in catabolism of the carbohydrate polymers of the detritus. Assuming equivalent rates of predation, a surface that is also a utilizable substrate supports a three- to fivefold more active microbial population.     

Pertussis toxin-induced lymphocytosis is associated with alterations in thymocyte subpopulations.

Pertussis toxin (Ptx), an important adjuvant for inducing certain organ-specific autoimmune diseases in mice, exerts multiple effects upon the immune system. In addition to its adjuvant effects, which include enhancement of delayed-type hypersensitivity and increased antibody production. Ptx elicits a marked lymphocytosis with a concomitant decrease in thymic weight. In vitro studies indicate that Ptx acts directly on thymocytes and that both susceptible and resistant populations exist. It is believed that these susceptible cells are released into the circulation and account, in part, for the T cell component of the lymphocytosis. We have used flow cytometry to analyze the CD4, CD8, and Thy-1 phenotypes of thymic and peripheral T cells from Ptx-treated mice. In the thymus, there is a dramatic decrease in the number of CD4+CD8+ (double positive) cells at all doses tested (0.25, 0.50, and 1.0 microgram) by day 4 after Ptx treatment. The double negative and single positive populations remain relatively constant. Analysis of Thy-1 expression reveals a significant reduction in Thy-1hi thymocytes, with little change in the Thy-1lo population. Thus Ptx primarily affects and depletes, in a dose-dependent fashion, thymic T cells with an immature phenotype. These results mimic those of corticosteroids, although neither prior adrenalectomy nor treatment with the antiglucocorticoid RU486 are able to prevent the effects of Ptx. In the periphery of Ptx-treated animals, the relative increase in the number of CD4+ T cells is more than that of CD8+ T cells. Double positive and Thy-1hi cells cannot be detected in appreciable numbers. These results are consistent with the concept that Ptx may drive immature thymocytes through accelerated maturation for release into the periphery as single positive, predominantly CD4+, Thy-1lo cells. Increased numbers of such cells may in part account for the immunopotentiating effects of Ptx, particularly as they relate to the induction of organ-specific autoimmune disease. Treatment with purified Ptx beta-oligomer fails to elicit any of the responses described above, indicating that the holotoxin is required for such activities.