Camptothecin inhibits both the cleavage and religation reactions of eukaryotic DNA topoisomerase I.

We investigated the mode of action of the antitumor drug, camptothecin, by use of a partly double-stranded suicide DNA substrate which enables uncoupling of the cleavage and religation half-reactions of topoisomerase I. The suicide DNA substrate contains a single topoisomerase I site at which SDS cleavage is strongly enhanced by camptothecin on normal double-stranded DNA. The results show that the religation reaction of topoisomerase I per se is strongly inhibited at this site compared to site that is only marginally affected by camptothecin on double-stranded DNA. This study hereby directly demonstrates that camptothecin-mediated stability of a topoisomerase I-DNA complex is sequence-dependent. The influence of camptothecin on the suicide cleavage reaction of topoisomerase I was also investigated. Surprisingly, the cleavage reaction per se is strongly inhibited by the drug. However, reformation of a cleavable suicide DNA substrate, which is fully double-stranded downstream from the cleavage position except for a nick, completely reverses the inhibitory effect of the drug on the cleavage reaction. The results suggest that the inhibitory effect of camptothecin on cleavage is due to a general decrease in the noncovalent interaction of topoisomerase I with partly double-stranded suicide DNA substrates. Based on the findings, a plausible model for camptothecin action is discussed.     

Identification of an N-terminal domain of eukaryotic DNA topoisomerase I dispensable for catalytic activity but essential for in vivo function.

We have found that deletion of a 70-amino acid domain, spanning from position 141 to 210 in the N-terminal part of human topoisomerase I, has no effect on the catalytic activity of the enzyme in vitro but suppresses the lethal consequence of overexpressing human topoisomerase I in a rad52 top1 Saccharomyces cerevisiae strain. By immunostaining, the 70-amino acid domain is shown to be necessary for nuclear location of topoisomerase I. We demonstrate that the nuclear localization signal from the SV40 large T antigen can substitute for the 70-amino acid domain, restoring both the lethal effect of overexpression and the correct subcellular localization of topoisomerase I. Thus, we have identified a domain in the N-terminal part of human topoisomerase I, nonessential for catalytic activity in vitro but serving an in vivo function by directing the enzyme to the nucleus. Based on sequence comparisons, we suggest that this domain is a conserved element in the apparently non-homologous N-terminal parts of yeast and human topoisomerase I.     

Comparative characterization of the iga gene encoding IgA1 protease in Neisseria meningitidis, Neisseria gonorrhoeae and Haemophilus influenzae

Cloning and sequencing of the IgA1 protease gene (iga) from Neisseria meningitidis strain HF13 showed an overall structure equivalent to iga genes from Neisseria gonorrhoeae and Haemophilus influenzae, although no region corresponding to the gonococcal α-peptide was evident. An additional 18 N. meningitidis and 3 H. influenzae iga genes were amplified by the polymerase chain reaction technique and sequenced corresponding approximately to the N-terminal half of the mature enzyme. Comparative analyses of a total of 29 iga genes showed that pathogenic Neisseria have iga genes with a significantly lower degree of heterogeneity than H. influenzae iga genes. Recombinational events indicated by mosaic-like structures corresponding to those found among N. gonorrhoeae protease genes were detected among N. meningitidis iga genes. One region showed characteristic differences in sequence and length which correlated with each of the different cleavage specificities. Meningococci were extremely conserved in this region with no evidence of recombination between isolates of different cleavage specificities. Sequences further downstream showed no obvious relationship with enzyme cleavage type. This region consisted of conserved areas interspersed with highly variable areas. Amino acid sequence homologies in the variable regions of meningococci reflected the antigenic types defined by using polyclonal neutralizing antibodies.     

Scanning electron microscopical observations on epidermal wound healing in the PlanarianDugesia tigrina

Summary Epidermal wound healing in regeneratingDugesia tigrina (Planaria) has been studied using scanning electron microscopy (SEM). The normal epidermal surface and its differentiations have been descrebed. Observations on living material reveal the highly dynamic state of the wound in invididual animals and its more or less continously changing size due to the state of activity of the animals. These observations show good agreement with the SEM studies, which allow a clear delineation of cellular details of the wound, the wound margins and the apposing epidermal regions. These details are described. The over-all picture of planarian wound healing that emerges is briefly as follows: Epithelization is characterized by absence of proliferation from the old intact epidermis. Variable contraction of smooth muscle cells reduces the wound size to a certain extent. Simultaneously with this and also during a longer period epidermal cells adjacent to the wound are extending and some become highly attenuated. These two processes together are only to a certain degree effective in wound closure because of a definite epidermal cell deficit which is reflected in the emergence of an epidermal wound edge reflecting the maximal contribution of these two processes to an attempt to close the wound. Complete epithelization is effected by the operation of a third mechanism: Recruitment of cell through flow of subjacent blastemal cells (including rhabdite-forming cells) along the wound border; these cells subsequently occupy a peripheral position in the wound. This process is supplemented by cell immigration and insertion into the adjacent old epidermis and in the wound cell sheet. Rhabdite-forming cells contribute predominantly to this process. Eventually integration between old epidermal cells and the newly recruited cells which differentiate into epidermal cells results in final epithelization. Complete wound healing is based on interactions between the epidermal cell system and the regenerating subepidermal membrane-connective tissue filament-muscle cell system.     

Immunofluorescent Immunoglobulin Differentiation of Vibrio Fetus Antibodies from Bovine Cervico-Vaginal Secretions

Reports on discrepancies between local and systemic immunity started to appear about 50 years ago (cf. Tomasi & Bienenstock 1968). Protection against infections has been shown in many cases to be closely related to the antibody content of external secretions and more or less independent from the serum antibody level.     

Plantago ser. Hispidulae, a taxonomic revision Knud Rahn

Plantago ser. Hispidulae Rahn belongs to subgen. Psyllium (Juss.) Harms sect. Gnaphaloides Barn. 5 species are recognized, they are all narrow–leaved annuals confined to the area west of the Andes. P. limensis Pers. occurs in Peru; P. litorea Phil., P. hispidula Ruiz & Pav., and P. rancagua Steud. in those parts of Chile with drought during the summer, and P. lundborgii Sparre on the island of San Ambrosio. Flowers are cleistogamic with small corolla lobes and small anthers, very rarely chasmogamic with larger corolla lobes and anthers. Experiments demonstrated that pollination is necessary for development of seeds in cleistogamic flowers, and that transfer of pollen from one such flower to another is almost impossible.