Effect of Alfa fibers on the mechanical and thermal properties of compacted earth bricks

International audienc

Nonhomologous RNA-RNA recombination events at the 3' nontranslated region of the Sindbis virus genome: hot spots and utilization of nonviral sequences.

The mechanism of RNA-RNA recombination at the 3' nontranslated region (3'NTR) of the Sindbis virus (SIN) genome was studied by using nonreplicative RNA precursors. The 11.7-kb SIN genome was transcribed in vitro as two nonoverlapping RNA fragments. RNA-1 contained the entire 11.4-kb protein coding sequence of SIN and also carried an additional 1.8-kb nonviral sequence at its 3' end. RNA-2 carried the remaining 0.26 or 0.3 kb of the SIN genome containing the 3'NTR. Transfection of these two fragments into BHK cells resulted in vivo RNA-RNA recombination and release of infectious SIN recombinants. Eighteen plaque-purified recombinant viruses were sequenced to precisely map the RNA-RNA crossover sites at the 3'NTR. Sixteen of the 18 recombinants were found to be genetically heterogeneous at the 3'NTR. Two major clustered sites within the 3'NTR of RNA-2 were found to be fused to multiple locations on the nonviral sequence of RNA-1, resulting in insertions of 10 to 1,085 nucleotides at the 3'NTR. Sequence analysis of crossover sites suggested only limited homology and heteroduplex-forming capability between substrate RNAs. Analysis of additional 23 recombinant viruses generated by mutagenized donor and acceptor templates supports the occurrence of recombination hot spots on donor templates. Introduction of a 17-nucleotide rudimentary replicase recognition signal in the acceptor template alone did not induce the polymerase to reinitiate at the 17-nucleotide signal. Interestingly, deletion of a 24-nucleotide hot spot locus on the donor template abolished crossover events at one of the two sites and allowed the polymerase to reinitiate at the 17-nucleotide replicase recognition signal inserted at the acceptor template. The possible roles of RNA-protein and RNA-RNA interactions in the differential regulation of apparent pausing, template selection, and reinitiation are discussed

Genome instability in BVDV: An examination of the sequence and structural influences on RNA recombination

AbstractThe cytopathogenic biotype of the pestivirus, bovine viral diarrhea virus, is frequently a product of nonhomologous recombination in the region of the genome encoding the viral NS2-NS3 proteins. The possibility that sequences or structures in this region contributed to a hotspot for RNA recombination was examined. A PCR-based strategy was used to examine viral genomic RNA isolated from tissue samples of cattle persistently infected with the noncytopathogenic biotype of the virus. Analysis of two different regions of the viral genome revealed that recombination was not restricted to particular sequences. Alignment of the genomic sequences undergoing recombination and examination of the predicted secondary structures of the participating RNAs revealed that the dissociation of partial, newly synthesized negative strand RNAs from the positive strand template occurred at many different sites on the molecule. Similarly, it appeared that the reassociation of the RNA polymerase complex with a second positive strand template was frequently influenced by short regions of homology between the nascent RNA strand and open secondary structures in the template molecule