A morphometric and ultrastructural study of lithium-induced changes in the medullary collecting ducts of the rat kidney

Summary Rats were given a lithium-containing diet (40 mmol/kg) to Study the effect of lithium on the structure of collecting ducts from the inner stripe of the outer medulla. The results show that there is a significant increase in the volume density of collecting ducts already after one week on this diet. The volume density of both intercalated and principal cells increases, whereas the volume density of mitochondria in the cytoplasm increases in the intercalated cells only. The increased volume of both principal and intercalated cells seems to be part of a general hyperplasia and hyperactivity of the collecting duct, which may in some way be related to the effects of lithium on vasopressinmediated water transport. The specific changes in the intercalated cells may be a consequence of the effects of lithium on distal nephron potassium and hydrogen ion transport in the distal nephron.     

Factors affecting malate dehydrogenase activity in freezing-thawing processes

Malate dehydrogenases from several sources show different behaviour when frozen-thawed in 100 mM sodium phosphate buffer, pH 7.4, containing chaotropic ions. The effects produced by the addition of various metabolites, protein concentration and buffer medium used on the loss of activity induced by the freezing-thawing process are reported. The major part of the loss of activity is caused by the formation of "wrong" aggregates of high mol. wt.     

Substrate specificity of DNA polymerases. I. Enzyme-catalysed incorporation of 5-''1-alkenyl)-2''-deoxyuridines into DNA.

A series of (E)-5-(1-alkenyl)-dUTPs as well as 5-vinyl-and (Z)-5-(1-propenyl)-dUTP have been synthesized to study steric requirements in DNA polymerase reactions. Experiments were carried out in E. coli DNA polymerase I Klenow fragment enzyme system. Substrates were characterized by KM and Vmax-values, initial incorporation rates as well as by total extent of incorporation of the analogues into poly(dA-dT) as a template-primer. Incorporation of the analogues could be best correlated with Vmax-values as well as the very similar initial incorporation rate values. Reactivity (Vmax/KM) showed no correlation with the extent of incorporation. 5-Vinyl-dUTP proved to be as good a substrate of the enzyme as dTTP, whereas (E)-5-(1-heptenyl)-and (E)-5-(1-octenyl)-dUTPs were very poor substrates, their incorporation was strongly limited and they also proved to be very efficient inhibitors of DNA replication, as shown by Ki-values. Substrate specificity of the Klenow enzyme can be explained by the steric hindrance of C-5 substituent, by the "orientational steric substituent effect" concept.     

Variability of colonial morphology in benomyl-induced morphological mutants from Candida albicans

Abstract Colonies of Candida albicans wild-type strain 1001 were white and glossy, and this character was rather stably maintained. In contrast, 2 benomyl (methyl benzimidazole-2-yl-carbamate)-induced mutant strains, B17 and B14, that grew as long filamentous forms and displayed a rough-wrinkled colonial phenotype, switched to other colonial morphologies at significant frequencies. Clonal populations of B17 segregated smooth or sectored (rough/smooth) colonies at a frequency of 1.85%, when plated in nutrient-agar. Strains derived from these rough or smooth segregants switched back to one or the other phenotype at similar frequencies. Colonial variability in C. albicans B14 was not restricted to spontaneous switching from rough to smooth or vice versa, but eventually other types of variants, characterized as 'wavy' and 'fuzzy' were obtained, and shown to have their own capacity to switch. Smooth variants, derived from B14, were essentiallt unicellular, whereas fuzzy strains consisted only of long thin filaments, wavy and rough clones apparently being intermediate in their degree of filamentation. It is concluded that the capacity for colonial variation shown to exist in natural isolates could be activated by benomyl in others, such as 1001, which are quite stable and do not switch colonial morphology spontaneously.     

G2 effects of DNA-repair inhibitors on chromatid-type aberrations in root-tip cells treated with maleic hydrazide and mitomycin C

In recent years the existence of a DNA-repair process in G2 has been proposed to explain the potentiating effects of DNA-repair inhibitors given in G2 on chromatid aberrations (CA) induced by S-dependent as well as S-independent DNA-damaging agents. In the present report, root-tip cells of Allium cepa were exposed to maleic hydrazide (MH) or mitomycin C (MMC) and post-treated in G2 with caffeine (Caff) and various inhibitors of DNA synthesis. No enhancement of chromosome damage was observed when Caff was present in G2, but hydroxyurea (HU) or 5-fluorodeoxyuridine (FdUrd) potentiated the frequencies of CA. A slight additional increase of CA frequencies was observed following treatment with Ara C and excess thymidine in G2. When MH-damaged cells were pulse-treated with Caff earlier during recovery, the yield of CA was enhanced. The earlier Caff was present following MH treatment, the stronger was the potentiation.     

A chromosomal genetic map of Rhizobium sp. NGR234 generated with Tn5-Mob

Summary Rhizobium sp. NGR234 in a fast-growing Rhizobium strain with a broad host range. The location and role of chromosomal genes involved in cellular metabolism or in the legume symbioses is unknown. We isolated a series of auxotrophic and antibiotic resistant mutants of NGR234 and utilized a chromosome mobilization system based on Tn5-Mob and pJB3JI; Tn5-Mob donor strains behaved like Hfr strains, transferring the chromosome polarly at high frequency from a fixed point of insertion. The use of four different strains with Tn5-Mob located at different nutritional loci in crosses with double auxotrophic recipients, allowed us to build up a circular linkage map of NGR234 based on relative recombination frequencies. Also, symbiotically important genes identified by site-directed mutagenesis, such as hemA and ntrA, could be located and mapped on the chromosome.Abbreviations Tc tetracycline - Sp spectinomycin - Rif rifampicin - Km kanamycin     

Restriction analysis of lambda EMBL3 background recombinants: occurrence of lambda phages carrying a head to tail oriented left arm DNA sequence

Summary Eight representative recombinant background clones of λEMBL3 were analysed usingKpnI,BamHI,SalI,EcoRI andHindIII digestion. We found that λEMBL3 carries its own left arm in theBamHI cloning site. In this way, recombinant molecules were found to be generated which can grow onEscherichia coli strain NM539. In all cases analysed, the left arm DNA was inserted in a head to tail orientation. Seven clones carried a restoredBamHI site at thecos site-BamHI site connection. In the region where the inserted left arm and the right arm were ligated,BamHI cloning produces a large palindromic sequence consisting of two polylinkers. ThisBamHI site was incompletely cleaved in all cases analysed. We assume that a part of the λ DNA molecule in this region shows a cruciform structure prohibiting recognition or cleavage of this site by restriction endonucleaseBamHI.