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Transposable elements are stretches of DNA that can move and multiply within the genome of an organism. The Caenorhabditis elegans genome contains multiple Tc1 transposons that jump in somatic cells, but are silenced in the germ line. Many mutants that have lost this silencing have also lost the ability to execute RNA interference (RNAi), a process whereby genes are suppressed by exposure to homologous double-stranded RNA (dsRNA). Here we show how RNAi causes transposon silencing in the nematode germ line. We find evidence for transposon-derived dsRNAs, in particular to the terminal inverted repeats, and show that these RNAs may derive from read-through transcription of entire transposable elements. Small interfering RNAs of Tc1 were detected. When a germline-expressed reporter gene is fused to a stretch of Tc1 sequence, this transgene is silenced in a manner dependent on functional mutator genes (mut-7, mut-16 and pk732). These results indicate that RNAi surveillance is triggered by fortuitous read-through transcription of dispersed Tc1 copies, which can form dsRNA as a result of ‘snap-back’ of the terminal inverted repeats. RNAi mediated by this dsRNA silences transposase gene expression. [ABSTRACT FROM AUTHOR]

RNA interference (RNAi) regulates gene expression by the cleavage of messenger RNA, by mRNA degradation and by preventing protein synthesis. These effects are mediated by a ribonucleoprotein complex known as RISC (RNA-induced silencing complex). We have previously identified four Drosophila components (short interfering RNAs, Argonaute 2 (ref. 2), VIG and FXR) of a RISC enzyme that degrades specific mRNAs in response to a double-stranded-RNA trigger. Here we show that Tudor-SN (tudor staphylococcal nuclease)-a protein containing five staphylococcal/micrococcal nuclease domains and a tudor domain-is a component of the RISC enzyme in Caenorhabditis elegans, Drosophila and mammals. Although Tudor-SN contains non-canonical active-site sequences, we show that purified Tudor-SN exhibits nuclease activity similar to that of other staphylococcal nucleases. Notably, both purified Tudor-SN and RISC are inhibited by a specific competitive inhibitor of micrococcal nuclease. Tudor-SN is the first RISC subunit to be identified that contains a recognizable nuclease domain, and could therefore contribute to the RNA degradation observed in RNAi. [ABSTRACT FROM AUTHOR]

Single nucleotide polymorphisms (SNPs) are valuable genetic markers of human disease. They also comprise the highest potential density marker set available for mapping experimentally derived mutations in model organisms such as Caenorhabditis elegans. To facilitate the positional cloning of mutations we have identified polymorphisms in CB4856, an isolate from a Hawaiian island that shows a uniformly high density of polymorphisms compared with the reference Bristol N2 strain. Based on 5.4 Mbp of aligned sequences, we predicted 6,222 polymorphisms. Furthermore, 3,457 of these markers modify restriction enzyme recognition sites ('snip-SNPs') and are therefore easily detected as RFLPs. Of these, 493 were experimentally confirmed by restriction digest to produce a snip-SNP map of the worm genome. A mapping strategy using snip-SNPs and bulked segregant analysis (BSA) is outlined. CB4856 is crossed into a mutant strain, and exclusion of CB4856 alleles of a subset of snip-SNPs in mutant progeny is assesed with BSA. The proximity of a linked marker to the mutation is estimated by the relative proportion of each form of the biallelic marker in populations of wildtype and mutant genomes. The usefulness of this approach is illustrated by the rapid mapping of the dyf-5 gene. [ABSTRACT FROM AUTHOR]

The solution structure of the dimeric N-terminal domain of HIV-2 integrase (residues 1–55, named IN1-55) has been determined using NMR spectroscopy. The structure of the monomer, which was already reported previously [Eijkelenboom et al. (1997) Curr. Biol., 7, 739–746], consists of four α-helices and is well defined. Helices α1, α2 and α3 form a three-helix bundle that is stabilized by zinc binding to His12, His16, Cys40 and Cys43. The dimer interface is formed by the N-terminal tail and the first half of helix α3. The orientation of the two monomeric units with respect to each other shows considerable variation. 15N relaxation studies have been used to characterize the nature of the intermonomeric disorder. Comparison of the dimer interface with that of the well-defined dimer interface of HIV-1 IN1-55 shows that the latter is stabilized by additional hydrophobic interactions and a potential salt bridge. Similar interactions cannot be formed in HIV-2 IN1-55 [Cai et al. (1997) Nat. Struct. Biol., 4, 567–577], where the corresponding residues are positively charged and neutral ones. [ABSTRACT FROM AUTHOR]

Shows that gene co-suppression in Caenorhabditis elegans is probably mediated by RNA molecules. Introduction of transgenic copies of a gene as resulting in a reduced expression of transgene and endogenous gene; Silencing of transposons from RNA interference and co-suppression; RNA-guided degradation of messenger RNA molecules.

Identifies Caenorhabditis elegans (C. elegans) as the first animal genome to be sequenced. Determination of the complete pattern of cell divisions which creates the somatic cells in the adult animal; Dependency of classical genetics on the isolation of mutants with clearly defined phenotypes; Possibility of transiently and genetically mutating genes in C. elegans.