Chymotrypsin-like enzymes are involved in sperm penetration through the vitelline coat of Ciona intestinalis egg

In Ciona intestinalis, sperm penetration through the egg vitelline coat is an essential event of fertilization. We investigated whether trypsin- and chymotrypsin-like enzymes are involved in this event. Inhibitors and peptide substrates for chymotrypsin-like enzymes blocked the overall process of fertilization in a concentration-dependent manner. The inhibitory activity was specifically exerted on the step of sperm penetration. Chymotrypsin-like protease activity was identified in spermatozoa with the fluorogenic synthetic substrate Suc-Ala-Ala-Phe-AMC, which was the most effective substrate in blocking sperm penetration. These data indicate that a chymotrypsin-like protease activity is a sperm lysin of Ciona intestinalis.     

Variation in nitrate metabolism in biovars of Pseudomonas solanacearum

A collection of 327 strains of Pseudomonas solanacearum , representing five biovars, was divisible into three groups on the basis of differences in nitrate metabolism. Nine strains (2.8%), of which seven were biovar 2 from bacterial wilt of potato, were nitrate reduction-deficient and failed to produce nitrite from nitrate by either of two methods of detection in five different media. A second group of 231 strains, comprising biovars 1 and 2 and a single biovar 3 strain, produced nitrite from nitrate and grew vigorously in the presence of nitrate under anaerobic conditions but were deficient in ability to denitrify. A third group comprising 57 strains of biovar 3, 28 of biovar 4 and one each of biovar 2 and 5 produced nitrite from nitrate and gave profuse growth and gas production from nitrate under anaerobic conditions. However, production of gas from nitrate (denitrification) was not a consistently reproducible property in some of the media tested. Gas production results were most reproducible when a semi-solid succinate/nitrate or glycerol/nitrate medium was used. Serial passage of four nitrate reduction-deficient isolates in nitrate medium did not restore ability to reduce nitrate.     

Electrical conductivity dispersion as a probe of membrane modifications in mouse polyomavirus infected cells in culture

In this report we investigate the inhibition of membrane conductivity, due to the murine polyomavirus infection in permissive cells in culture. We define experimental conditions to have reproducible results and demonstrate that the intensity of the effects on the cell membrane, depends upon the virus titer used in the infection. Finally, the virus dependent effects disappear if the infection is performed in the presence of a drug that inhibits polymavirus DNA replication.     

Worm burdens in schistosome infections

Schistosomiasis, caused by fluke worms of Schistosoma spp, is one of the most common tropical diseases. Despite decades of research and progress towards the control of the disease, many aspects of the dynamics of infection and immunity remain unresolved. There is, in fact, not even an approximate measure of how many worms are harboured by infected humans. Epidemiological, mathematical and biomedical arguments indicate that individual worm burdens in endemic areas number hundreds to thousands of adult schistosomes, instead of the few to dozens generally assumed on the basis of available autopsy data. As Bruno Gryseels and Sake de Vlas here discuss, this hypothesis has important consequences for research and control, as many constants in schistosomiasis research have to be reconsidered.     

Processing of the intron-encoded U16 and U18 snoRNAs: the conserved C and D boxes control both the processing reaction and the stability of the mature snoRNA.

A novel class of small nucleolar RNAs (snoRNAs), encoded in introns of protein coding genes and originating from processing of their precursor molecules, has recently been described. The L1 ribosomal protein (r-protein) gene of Xenopus laevis and its human homologue contain two snoRNAs, U16 and U18. It has been shown that these snoRNAs are excised from their intron precursors by endonucleolytic cleavage and that their processing is alternative to splicing. Two sequences, internal to the snoRNA coding region, have been identified as indispensable for processing the conserved boxes C and D. Competition experiments have shown that these sequences interact with diffusible factors which can bind both the pre-mRNA and the mature U16 snoRNA. Fibrillarin, which is known to associate with complexes formed on C and D boxes of other snoRNAs, is found in association with mature U16 RNA, as well as with its precursor molecules. This fact suggests that the complex formed on the pre-mRNA remains bound to U16 throughout all the processing steps. We also show that the complex formed on the C and D boxes is necessary to stabilize mature snoRNA.     

Loss of the ORF in the SSUrDNA group I intron of one Naegleria lineage.

We have found a Naegleria lineage in which the SSUrDNA contains a group I intron with a length of 375 nucleotides. This is a unique finding because all group I introns detected until now in Naegleria are 1.3 kilobases long and contain an open reading frame coding for 245 amino acids. Sequence data show that the 375 nucleotide-long intron is at the same place in the SSUrDNA as, and is descendant from, the 1.3 kilobase group I intron present in other species of Naegleria. Our data indicate that in one lineage of Naegleria the group I intron lost part of its DNA that is not contributing to the secondary structure but that carries the open reading frame. The amoeboflagellate genus Naegleria contains strains without the intron and strains with the intron, with or without an open reading frame. Therefore, this genus provides a unique opportunity to study the function and evolution of both the group I intron and the open reading frame.