Gene transfer to the nucleus and the evolution of chloroplasts

Photosynthetic eukaryotes, particularly unicellular forms, possess a fossil record that is either wrought with gaps or difficult to interpret, or both. Attempts to reconstruct their evolution have focused on plastid phylogeny, but were limited by the amount and type of phylogenetic information contained within single genes. Among the 210 different protein-coding genes contained in the completely sequenced chloroplast genomes from a glaucocystophyte, a rhodophyte, a diatom, a euglenophyte and five land plants, we have now identified the set of 45 common to each and to a cyanobacterial outgroup genome. Phylogenetic inference with an alignment of 11,039 amino-acid positions per genome indicates that this information is sufficient--but just rarely so--to identify the rooted nine-taxon topology. We mapped the process of gene loss from chloroplast genomes across the inferred tree and found that, surprisingly, independent parallel gene losses in multiple lineages outnumber phylogenetically unique losses by more that 4:1. We identified homologues of 44 different plastid-encoded proteins as functional nuclear genes of chloroplast origin, providing evidence for endosymbiotic gene transfer to the nucleus in plants.     

Specific inhibition of herpesvirus ribonucleotide reductase by synthetic peptides

Ribonucleotide reductase is an essential enzyme for DNA synthesis in all prokaryotic and eukaryotic cells; it catalyses the reductive conversion of ribonucleotides to deoxyribonucleotides. Several herpesviruses including herpes simplex virus type 1 (HSV-1), HSV-2, pseudorabies virus (PRV), equine herpesvirus type 1 (EHV-1) and Epstein-Barr virus (EBV) have been found to induce novel ribonucleotide reductase activities. There is evidence that the HSV-1 ribonucleotide reductase activity is virus-encoded and essential for virus replication. This makes herpesvirus ribonucleotide reductases potential targets for antiviral chemotherapy. The HSV-1-encoded enzyme consists of two subunits: V136, the large subunit of relative molecular mass (Mr) 136,000 (136K) (RR1), which has been shown to be essential for enzyme activity, and V38, the small subunit (RR2) which forms a complex with the large subunit and is also likely to be essential for enzyme activity. Two particular features of the enzyme make it an attractive antiviral target. First, there is evidence for a common, highly conserved herpesvirus ribonucleotide reductase and second, the interaction between the large and small subunits may itself be exploitable. Here we identify a synthetic peptide which specifically inhibits the activity of virus-induced enzyme. We deduce that the mechanism of inhibition involves interference with the normal interaction between the two types of subunit.     

Experimental allergic encephalomyelitis in T-lymphocyte deficient rats.

Thymectomized, lethally irradiated rats reconstituted with syngeneic bone marrow were injected with rat brain in complete Freund adjuvant mixture. Both, they and sham-thymectomized, irradiated and bone marrow protected rats displayed a higher incidence of leg paralysis than normal non-irradiated animals. Thymectomy lowered the incidence of the disease.