Psychologie und Psychiatrie

International Journal of Legal Medicine -     

Sequences and replication of genomes of the archaeal rudiviruses SIRV1 and SIRV2: relationships to the archaeal lipothrixvirus SIFV and some eukaryal viruses

The double-stranded DNA genomes of the viruses SIRV1 and SIRV2, which infect the extremely thermophilic archaeon Sulfolobus and belong to the family Rudiviridae, were sequenced. They are linear, covalently closed at the ends, and 32,312 and 35,502 bp long, respectively, with an A+T content of 75%. The genomes of SIRV1 and SIRV2 carry inverted terminal repeats of 2029 and 1628 bp, respectively, which contain multiple direct repeats. SIRV1 and SIRV2 genomes contain 45 and 54 ORFs, respectively, of which 44 are homologous to one another. Their predicted functions include a DNA polymerase, a Holliday junction resolvase, and a dUTPase. The genomes consist of blocks with well-conserved sequences separated by nonconserved sequences. Recombination, gene duplication, horizontal gene transfer, and substitution of viral genes by homologous host genes have contributed to their evolution. The finding of head-to-head and tail-to-tail linked replicative intermediates suggests that the linear genomes replicate by the same mechanism as the similarly organized linear genomes of the eukaryal poxviruses, African swine fever virus and Chlorella viruses. SIRV1 and SIRV2 both contain motifs that resemble the binding sites for Holliday junction resolvases of eukaryal viruses and may use common mechanisms for resolution of replicative intermediates. The results suggest a common origin of the replication machineries of the archaeal rudiviruses and the above-mentioned eukaryal viruses. About 1/3 of the ORFs of each rudivirus have homologs in the Sulfolobus virus SIFV of the family Lipothrixviridae, indicating that the two viral families form a superfamily. The finding of inverted repeats of at least 0.8 kb at the termini of the linear genome of SIFV supports this inference.     

Retinal pigment epithelium is protected against apoptosis by alphaB-crystallin

PURPOSE: The degeneration of retinal pigment epithelial (RPE) cells is considered to be a crucial event in the pathophysiology of age-related macular degeneration (AMD). Cumulative oxidative damage has been implicated in the development of the changes seen in AMD. The present study was undertaken to evaluate the expression of the small heat shock protein alphaB-crystallin in the RPE in response to oxidative stress and to explore whether alphaB-crystallin expression confers an antiapoptotic cytoprotective effect on RPE cells. METHODS: Native human RPE cells from the macula and retinal periphery were analyzed by RT-PCR and Western blot analysis for expression of alphaB-crystallin. Monolayer cultures of human RPE cells were stressed by heat shock (42 degrees C for 20 minutes) or oxidant-mediated injury (50-300 micro M H(2)O(2) for 1 hour). Induction of alphaB-crystallin and the corresponding mRNA was assessed by Western and Northern blot analyses. To study the cytoprotective effect of alphaB-crystallin, human RPE cells were transfected with either a neomycin-selectable expression vector containing alphaB-crystallin cDNA or a control vector without alphaB-crystallin cDNA. Caspase-3 activity was determined by observing the cleavage of a colorimetric peptide substrate. Cell viability was quantified by combined propidium iodide and Hoechst 33342 staining. RESULTS: alphaB-crystallin is constitutively expressed in RPE under in vivo and in vitro conditions. Western blot analysis of freshly isolated RPE showed greater baseline expression levels in RPE derived from the macular area than in that from the more peripheral regions. Heat shock treatment and oxidative stress caused a significant increase in alphaB-crystallin mRNA and protein. Oxidant-mediated injury in RPE cells with baseline expression levels of alphaB-crystallin resulted in apoptotic cell death, as measured by caspase-3 activity, whereas RPE cells that had been stably transfected with alphaB-crystallin were more resistant to H(2)O(2)-induced cellular injury. CONCLUSIONS: alphaB-crystallin may function as a stress-inducible antiapoptotic protein in human RPE and is inducible by oxidative stress, a condition implicated in the pathogenesis of AMD. Overexpression of alphaB-crystallin may be an important mechanism for the RPE to prevent apoptotic cell death in response to cellular stress.     

A novel lipothrixvirus, SIFV, of the extremely thermophilic crenarchaeon Sulfolobus

We describe a novel lipothrixvirus, SIFV, of the crenarchaeotal archaeon Sulfolobus islandicus. SIFV (S. islandicus filamentous virus) has a linear virion with a linear double-stranded DNA genome. These two features coincide in several crenarchaeotal but not in any other viruses. The SIFV core is formed by a zipper-like array of DNA-associated protein subunits and is covered by a lipid envelope containing host lipids. We sequenced approximately 96% of the virus genome excepting the DNA termini, which were modified in an unusual, yet uncharacterized, manner. Both, the 5' and the 3' DNA termini were insensitive to enzymatic degradation and labelling. Two open reading frames (ORFs) of the SIFV genome are likely to encode helicases and resemble uncharacterized ORFs from other archaea in sequence. Three ORFs showed sequence similarity with each other and each contained a glycosyl transferase motif. Another ORF of the SIFV genome showed significant sequence similarity to the ORF a291 from the well characterized, spindle-shaped Sulfolobus virus SSV1. Due to its structure, SIFV is classified as a lipothrixvirus.     

The genome of the archaeal virus SIRV1 has features in common with genomes of eukaryal viruses

The virus SIRV1 of the extremely thermophilic archaeon Sulfolobus has a double-stranded DNA genome similar in architecture to the genomes of eukaryal viruses of the families Poxviridae, Pycodnaviridae, and Asfarviridae: the two strands of the 32,301 bp long linear genome are covalently connected forming a continuous polynucleotide chain and 2029 kb long inverted repeats are present at the termini. Very likely it also shares with these viruses mechanisms of initiation of replication and resolution of replicative intermediates.     

Archaebacterial DNA-dependent RNA polymerases testify to the evolution of the eukaryotic nuclear genome.

Genes for DNA-dependent RNA polymerase components B, A, and C from the archaebacterium Sulfolobus acidocaldarius and for components B", B', A, and C from the archaebacterium Halobacterium halobium were cloned and sequenced. They are organized in gene clusters in the order above, which corresponds to the order of the homologous rpoB and rpoC genes in the corresponding operon of the Escherichia coli genome. Derived amino acid sequences of archaebacterial components A and C were aligned with each other and with the sequences of corresponding (largest) subunits from the archaebacterium Methanobacterium thermoautotrophicum, with sequences of various eukaryotic nuclear RNA polymerases I, II, and III, and with the sequence of the beta' component from E. coli polymerase. The archaebacterial genes for component A are homologous to about the first two-thirds of genes for the eukaryotic component A and the eubacterial component beta', and the archaebacterial genes for component C are homologous to the last third of the genes for the eukaryotic component A and the eubacterial component beta'. Unrooted phylogenetic dendrograms derived from both distance matrix and parsimony analyses show the archaebacteria are a coherent group closely related to the eukaryotic nuclear RNA polymerase II and/or III lineages. The eukaryotic polymerase I lineage appears to arise separately from a bifurcation with the eubacterial beta' component lineage.