[How great is the risk of hepatitis due to travel? Retrospective study in the region of Zurich 1971-1976]

Between 1971 and May 1976 221 adult persons originating from the region of Zurich (Switzerland) developed acute viral hepatitis within the incubation period after a usually brief trip abroad. In those returning from European countries the ratio of HBsAg positive and negative infections was similar to that in the Canton of Zurich. From other continents the proportion of non-B hepatitis was 66-94%. On the basis of travel statistics the risk of this disease was assessed as highest in West Africa and Mexico; trekkers are especially exposed. The indication and dosage for immunoprophylaxis are discussed in detail.

[Risk groups in travel to tropical countries within the frame of mass tourism]

More than 10,000 tourists returning from tropical countries have been asked about health problems during their stay abroad. Preliminary results from the first 5,550 questionnaires indicate that 74,8% had complaints of any kind concerning their health and 13,6% can be considered as having been ill. The frequency of complaints and illness in relation to different variables is shown and the possibility of definition of high risk groups is being discussed.

Alterations of activities of ribonucleases and polyadenylate polymerase in synchronized mouse L cells

The activities of the three known catabolic and the one anabolic polyadenylate enzymes have been determined in synchronized L5178y cells: endoribonuclease, exoribonuclease, 5'-nucleotidase and poly(A) polymerase (Mg2+-dependent). These four enzymes were found primarily in the nuclear fraction. The activity of poly(A) polymerase remains essentially constant during the transition from G1 to S phase. However, the poly(A) catabolic enzyme activities increase parallel with DNA synthesis; the endoribonuclease activity increases 4-fold during G1 to S phase, the exoribonuclease and the nucleotidase activities increasing 30-fold and 16-fold. During the S phase the poly(A)-degrading enzymes are far more active than the poly(A)-synthesizing activity of poly(A) polymerase. We conclude that in L5178y cells the poly(A)-degrading enzymes probably function in regulation of the post-transcriptional net-polyadenylation of heterogeneous nuclear RNA during the phase of DNA synthesis.

Endoribonuclease IV. 2. Further investigation on the specificity

The poly(A)-specific endoribonuclease IV produces oligo(A) fragments of a chain length of 10 AMP nucleotides. One enzyme molecule performs 1700 cleavages per min; the cleavages occur randomly. The endoribonuclease IV is a nuclear enzyme which is present in the oviduct of quails in a concentration of 40 000 enzyme molecules per cell. Poly(A) segments on mRNA are selectively hydrolyzed by endoribonuclease IV; the poly(A)-free part of the RNA is not affected. After incubation with the enzyme, a residual oligo(A) stretch of 5 AMP nucleotides remains on poly(A)-rich RNA. The endoribonuclease IV does not disintegrate the polyribosomal complex after incubation in vitro and the enzyme has also no influence on the translational capacity of a cell-free protein-synthesizing system.

Influence of formycin B on polyadenosine diphosphoribose synthesis in vitro and in vivo

Formycin B inhibited growth of L5178Y mouse leukemia cells in concentrations of less than twice the concentration that inhibits cell proliferation at 50% by cytostasis; at higher concentrations (more than twice the 50% concentration mentioned), the cells were killed. In cells treated with the concentration that inhibits cell proliferation at 50%, the average cell volume did not change. The formycin B inhibitory effect on cell proliferation was reduced by coincubation with nicotinamide adenine diphosphate or adenosine. The biosyntheses of DNA,RNA, and protein in whole cells were sensitively inhibited by formycin B as checked by incorporation studies with radioactive precursors. In addition, the formation of polyadenosine diphosphoribose was reduced even with higher sensitivity; in particular the extent of adenosine diphosphate ribosylation of histone subfraction H1 was reduced. Formycin B has been shown to be an inhibitor for the polyadenosine diphosphoribose polymerase, isolated from oviduct nuclei of quails. Both the chromatin-bound and the soluble enzyme are inhibited competitively; the relative affinity (Ki/Km) of formycin B to the polyadenosine diphosphoribose polymerase is 1.5.