Hybrid plasmid with bacterial and fungal markers carrying the denV gene of T4 phage and restoring the UV-resistance of E. coli uvrA

The hybrid plasmid pYBP2 with bacterial (ampR), yeast (LEU2) and bacteriophage T4 (denV) genes has been constructed. The plasmid transformed Escherichia coli CSR603 uvrA recA ampS leuA phr- to ampicillin resistance, leucine independence, UV-resistance similar to the one of uvrA+ recA strain. Cell-free extracts of transformed Escherichia coli cells contain low level of ultraviolet-endonuclease activity in contrast to nontransformed cells containing no enzyme.     

The structure of products of modification of nucleotides and DNA by ethyleneimine and thio-TEPA

Previously undescribed products of dGMP, GMP, AMP, dCMP and TMP aminoethylation by ethylenimine and N,N',N"-triethylenethiophosphoamide (thio-TEPA) have been obtained and shown to be aminoethyl esters of nucleotides with the free or substituted amino group. In case of dGMP and GMP ethylenimine and tio-TEPA alkylate not only phosphate but also the base residue at the N7 position. The 7-aminoethyl derivatives of dGMP and GMP, which thio-TEPA afforded, were characterized whereas the corresponding ethylenimine derivatives are decomposed under alkaline conditions in the course of the isolation. Possible reasons of extreme instability of these compounds are given. For the first time the ability of thio-TEPA to alkylate DNA at position 7 of guanine residue is shown by means of the luninescence method.     

Entry and release of transmissible gastroenteritis coronavirus are restricted to apical surfaces of polarized epithelial cells.

The transmissible gastroenteritis coronavirus (TGEV) infects the epithelial cells of the intestinal tract of pigs, resulting in a high mortality rate in piglets. This study shows the interaction of TGEV with a porcine epithelial cell line. To determine the site of viral entry, LLC-PK1 cells were grown on permeable filter supports and infected with TGEV from the apical or basolateral side. Initially after plating, the virus was found to enter the cells from both sides. During further development of cell polarity, however, the entry became restricted to the apical membrane. Viral entry could be blocked by a monoclonal antibody to the viral receptor aminopeptidase N. Confocal laser scanning microscopy showed that this receptor protein was present at both the apical and basolateral plasma membrane domains just after plating of the cells but that it became restricted to the apical plasma membrane during culture. To establish the site of viral release, the viral content of the apical and basolateral media of apically infected LLC-PK1 cells was measured by determining the amount of radioactively labelled viral proteins and infectious viral particles. We found that TGEV was preferentially released from the apical plasma membrane. This conclusion was confirmed by electron microscopy, which demonstrated that newly synthesized viral particles attached to the apical membrane. The results support the idea that the rapid lateral spread of TGEV infection over the intestinal epithelia occurs by the preferential release of virus from infected epithelial cells into the gut lumen followed by efficient infection of nearby cells through the apical domain.     

Ecological correlates of seed persistence in soil in the north-west European flora

1 Using the data in a recently published seed bank database for north-west Europe, we describe how a species' seed bank behaviour can be characterized by a single 'longevity index', and investigate how representative the information in the database is of the north-west European flora. We also test the hypotheses that seeds of short-lived species are more persistent than those of long-lived species, and long-lived seeds are characteristic of species living in disturbed habitats.
2 The data are not representative of the north-west European flora as a whole; they are a fair reflection of a research effort that has been largely directed towards grassland and arable weeds. Data for rare species, non-agricultural habitats in general and wetlands, rocky habitats and native woodland in particular, are scarce or absent.
3 Annuals and biennials almost always have more persistent seeds than related perennials, and this difference is most striking when, as in Anagallis arvensis and Aphanes arvensis , the short-lived species have moved well away from the 'core' habitat of the family. Confamilial monocarps and polycarps do not differ consistently in seed mass.
4 Gradients of habitat disturbance are accompanied by predictable changes in seed persistence, which are themselves often (but not always) accompanied by parallel shifts in seed size. These results suggest that increasing habitat disturbance (i.e. increasing density-independent mortality) always selects for increased seed persistence, confirming both theory and previous analyses. However, increased seed persistence is not always associated with reduced seed size. This is because persistence depends not only on seed size, but on other traits, many of them physiological. In many habitats the probability of seed burial is strongly linked to seed size and shape, but in arable habitats cultural practices have broken this link.     

Soil nutrient input effects on seed longevity: a burial experiment with fen-meadow species

1. Effects of high nutrient input on the longevity and viability of buried seed are examined. Seeds of 17 fen-meadow species were buried in nylon mesh bags at four sites in the Netherlands and one site in Great Britain in plots to which N, P, K fertilizers are applied. Prior to burial germination tests were conducted on the seeds of each species. This paper describes the results of the viability tests on the seeds that were exhumed after one and 2 years of burial.
2. The percentage of seeds that germinated after 1 year of burial was significantly lower than the pre-burial percentage for the majority of the species. After 2 years of burial the germination percentage further decreased. A few species, such as the Carex species, did, however, show an increase in germination percentage indicating that the burial conditions allowed dormancy controls to be broken.
3. Differences in the edaphic conditions between the sites appeared to affect germination percentages after 1 year of burial. A difference in germination response between sites was observed for Carex acutiformis, Filipendula ulmaria and Lychnis flos-cuculi .
4. A significantly higher germination percentage was found at the Great Britain site for F. ulmaria in the phosphate treatment compared with the potassium treatment and the control after 1 year of burial. In contrast to many literature assessments no significant effects of fertilizer application was found after 2 years.
5. For all sites, except one in the Netherlands, the total number of seeds that germinated was lower in 1996 than in 1995.     

Ultraviolet-endonuclease activity in cell extracts of Saccharomyces cerevisiae mutants defective in excision of pyrimidine dimers.

Cell-free extracts of ultraviolet-sensitive mutants of Saccharomyces cerevisiae defective in excision of pyrimidine dimers, rad1, rad2, rad3, rad4, rad10, and rad16, as well as the extracts of the wild-type strain RAD+, display ultraviolet-endonuclease activity.     

Salmonella antigens inBacterium coli and paragglutination

Summary The phenomenon of paragglutination with typhoid serum ofB. coli from the intestines of healthy persons and of patients suffering from typhoid or paratyphoid fever was observed and studied. Evidence could be obtained that the paragglutination was to be attributed to the presence of a commonSalmonella antigen (XXVIII), so that it is wrong to make a distinction between paragglutination and co-agglutination. Salmonella antigens were found in various combinations withB. coli and different combinations could also be ascertained with the same person.The attention is drawn to the presence of the Vi-antigen withB. coli, also from healthy persons, and the possibility of its connection with the Vi-agglutinin in the blood of healthy persons is pointed at.     

Purification and properties of deoxyribonucleic acid polymerase from Bacillus stearothermophilus.

Deoxyribonucleic acid polymerase I was purified from Bacillus stearothermophilus to 50 to 70% homogeneity. Its molecular weight was 76,000. The enzyme was insensitive to sulfhydryl blocking agents and showed maximal activity at 60 degrees C, pH 8 to 9, 0.25 M KCl, and 0.02 M MgSO4. The rate of heat inactivation of the deoxyribonucleic acid polymerase followed first-order kinetics with a half-life of 90 min at 60 degrees C; the addition of 0.05% bovine serum albumin protected the enzyme, which could be heated for 180 min without loss of activity. The ratios of polymerase to nuclease activities were about 20 for 5'-3' exonuclease and more than 500 for 3'-5' exonuclease. The Km for deoxyribonucleoside-5'-triphosphates was 7 microM.