Host interference with expression of the lambda N gene product

We have searched among E. coli M72 (D, bio11cI857H1) temperature resistant survivors and have found two bacterial mutants, gro100 and gro101 which block λiλ and λi⁴³⁴ phage development but allow growth of their N-independent derivatives λiλ nin and λi⁴³⁴nin. It is not known yet whether these two mutants interfere with the production of the N gene product or with its function. At least part of the gro genotype maps at 12′ of the E. coli genetic map and is co-transductible by Pl with the lac locus.     

Photosynthetic electron transport interaction of xanthorrhizol isolated from Iostephane heterophylla and its derivatives

A bioactivity-guided chemical study of Iostephane heterophylla (Asteraceae) led to the isolation of xanthorrhizol (1) as the compound that causes inhibition of ATP synthesis, H⁺-uptake and electron flow from water to methylviologen (basal, phosphorylating and uncoupled) in freshly lysed spinach chloroplasts, thus acting as an inhibitor of the Hill reaction. Acetyl (2), dihydro (3) and acetyl-dihydro (4) derivatives were synthesized. It was found that 4 was less active than 1 and 2 in ATP synthesis, whereas 3 was the most potent inhibitor of the Hill reaction and was also an inhibitor of H⁺-ATPase. Studies of the photosynthetic partial redox reactions from PQ to MV indicated that 1 partially inhibited the PQ pool, but that 3 did not. However, both inhibited the uncoupled electron transport in PSII from water to DCBQ. Uncoupled electron flow from water to silicomolybdate was completely inhibited by 3 and partially by 1. The reaction from DPC to DCPIP was inhibited by both 1 and 3. These results indicate that the inhibition site is located within PSII for 1 and 3 as was corroborated by fluorescence decay data.     

The change of behaviour of two strains of Leishmania after cultivation in a defined medium

Attempts have been made to characterize two strains of Leishmania that became infective to golden hamsters only after they had been maintained for several years in a chemically defined culture medium. Observations were made on the growth rates of promastigotes in vitro, course of infection in hamsters, morphology of amastigotes, and electrophoretic mobility patterns of eight isoenzymes. Information was obtained about the buoyant densities of n-DNA and k-DNA, and one strain was tested against monoclonal antibodies. The identity of both strains remains obscure.     

Fishery, seasonal abundance and mortality of grey mullets (Pisces: Mugilidae) in Negombo Lagoon, Sri Lanka

The seasonal abundance and instantaneous natural and fishing mortalities of six species of grey mullets, namely Liza subviridis, L. macrolepis, L. tade, Mugil cephalus, Valamugil buchanani and V. cunnesius were studied as a prelude for the management of their fishery in Negombo lagoon (7°10′N and 79°50′E). L. subviridis was the most abundant of the grey mullet species in the commercial catches and accounted for 37% of the total grey mullet catch. M. cephalus was the least abundant and constituted 6%. The annual catch of grey mullets was estimated to be around 23 000 kg (5.67 kg/ha); about 40 % of the total fish landings of the lagoon. The seasonal variation in the catch of different species of grey mullets appear to be related to their breeding seasons and spawning migrations. The highest value for instantaneous natural and fishing mortalities, which were 1.04 and 0.94 respectively were obtained for V. cunnesius. The lowest values for instantaneous natural and fishing mortalities which were 0.51 and 0.19 respectively were obtained for M. cephalus. The exploitation ratios calculated were less than 0.5 for all species other than L. tade which suggest that the grey mullet populations excluding L. tade in this lagoon may presently be underexploited.     

Induction of SOS and adaptive responses by alkylating agents in Escherichia coli mutants deficient in 3-methyladenine-DNA glycosylase activities

The induction of SOS and adaptive responses by alkylating agents was studied in Escherichia coli mutants tagA and alkA deficient in 3-methyladenine-DNA glycosylase activities. The SOS response was measured using an sfiA::lacZ operon fusion. The sfiA operon, in the double mutant tagA alkA, is induced at 5-50-fold lower concentrations of all tested methylating and ethylating compounds, as compared to the wild-type strain. In all cases, the tagA mutation, which inactivates the constitutive and specific 3-alkyladenine-DNA glycosylase I (TagI), sensitizes the strain to the SOS response. The sensitization effect of alkA mutation, which inactivates the inducible 3-alkyladenine-DNA glycosylase II (TagII), is observed under conditions which allow the induction of the adaptive response. We conclude that the persistence of 3-methyladenine and 3-ethyladenine residues in DNA most likely leads to the induction of the SOS functions. In contrast, the adaptive response, evaluated by O6-methylguanine-DNA methyltransferase activity in cell extracts, was not affected by either tagA or alkA mutations. The results suggest that the SOS and adaptive responses use different alkylation products as an inducing "signal". However, adaptation protein TagII inhibits the induction of the SOS response to some extent, due to its action at the level of signal production. Finally, we provide conditions to improve short-term bacterial tests for the detection of genotoxic alkylating agents.     

Seasonal changes in the activities of glycolytic enzymes from liver and skeletal muscle of Rana perezi

Glycogen phosphorylase (GP), Hexokinase (HK), Phosphofructokinase (PFK), Pyruvate kinase (PK) and Lactate dehydrogenase (LDH) activities from skeletal muscle and liver were measured in Rana perezi for the four seasons of the year. Skeletal muscle showed a decrease in PFK, PK and LDH activity during winter and summer. Liver displayed an increase in GP activity in spring and in PK and LDH in autumn.     

Subcellular Location and Neuronal Release of Diazepam Binding Inhibitor

Diazepam binding inhibitor (DBI), a peptide located in CNS neurons, blocks the binding of benzodiazepines and beta-carbolines to the allosteric modulatory sites of gamma-aminobutyric acid (GABAA) receptors. Subcellular fractionation studies of rat brain indicate that DBI is compartmentalized. DBI-like immunoreactivity is highly enriched in synaptosomes obtained by differential centrifugation in isotonic sucrose followed by a Percoll gradient. In synaptosomal lysate, DBI-like immunoreactivity is primarily associated with synaptic vesicles partially purified by differential centrifugation and continuous sucrose gradient. Depolarization induced by high K+ levels (50 mM) or veratridine (50 microM) released DBI stored in neurons of superfused slices of hypothalamus, hippocampus, striatum, and cerebral cortex. The high K+ level-induced release is Ca2+ dependent, and the release induced by veratridine is blocked by 1.7 microM tetrodotoxin. Depolarization released GABA and Met5-enkephalin-Arg6-Phe7 together with DBI. DBI is also released by veratridine depolarization, in a tetrodotoxin-sensitive fashion, from primary cultures of cerebral cortical neurons, but not from cortical astrocytes. Depolarization fails to release DBI from slices of liver and other peripheral organs. These data support the view that DBI may be released as a putative neuromodulatory substance from rat brain neurons.     

DNA-protein flow cytometric analysis in non-Hodgkin lymphoma

A flow cytometric study of DNA and protein contents was performed on cell suspensions obtained from 73 adult patients with non-Hodgkin lymphoma. Bivariate analysis identified a second subpopulation, not revealed by DNA determination, in 25% of the tumors. Protein heterogeneity was more frequently observed in diffuse than in nodular histology according the Rappaport classification and in high-grade than in low-grade malignancy tumors by the Kiel classification and the Working Formulation, but it was not related to ploidy or cell proliferative rate. The presence of an additional subpopulation, detected by protein analysis, defined as monoclonal by DNA analysis, could adversely affect clinical outcome in terms of response to treatment and overall survival.