Members and prospective members of the family Phycodnaviridae are large icosahedral, dsDNA (180 to 560 kb) viruses that infect eukaryotic algae. The genomes of two phycodnaviruses have been sequenced: the 331 kb genome of Paramecium bursaria chlorella virus (PBCV-1) and more recently, the 336 kb genome of the Ectocarpus siliculosus virus (EsV-1). EsV-1 has approximately 231 protein-encoding genes whereas, the slightly smaller PBCV-1 genome has 11 tRNA genes and approximately 375 protein-encoding genes. Surprisingly, the two viruses only have 33 genes in common, of which 17 have no counterparts in the databases. The low number of homologous genes between the two viruses can probably be attributed to their different life styles. PBCV-1 is a lytic virus that infects a unicellular, endosymbiotic freshwater green alga whereas, EsV-1 is a lysogenic virus that infects a free-living filamentous marine brown alga. Furthermore, accumulating evidence indicates that the phycodnaviruses and their genes are ancient, thus allowing significant differences to have evolved. This review briefly describes some of the biological properties of the phycodnaviruses, focusing on PBCV-1 and EsV-1, and then compares their genomes.

The synthesis of a series of enantiomerically pure, C,-symmetric 4,4,5,5'-tetrahydro-2,2'-methylenebis[oxazoles] and 4,4',5,5'-tetrahydro-2,2'-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91 % ee). Tetrahydrobi(oxazo1e)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH=CHCH(OAc)Ph with NaHC(COOMe),).Introduction. -In our previous papers in this series [l-31, we have reported on the synthesis and application of chiral semicorrins 1, a class of bidentate ligands specifically designed for enantioselective control of metal-catalyzed reactions. Essential structural features of the semicomns 1 are the conformationally rigid ligand framework and the C,-symmetric arrangement of the stereogenic centers in close proximity to the coordination site. In a metal complex, the substituents at the stereogenic centers effectively shield the metal ion from two opposite directions and, therefore, should have a distinct effect on the stereochemical course of a reaction taking place in the coordination sphere. So far, we have found two promising areas of application for semicorrin ligands: [Cu(semicorrinato)]-catalyzed cyclopropane formation from olefins and diazo compounds (up to 97% ee [ 1][3]) and [Co(semicorrinato)]-catalyzed conjugate reduction of a$-unsaturated carboxylic esters and amides (up to 99% ee [21[31).Symmetric 4,4',5,5'-tetrahydro-2,2'-methylenebis[oxazoles] 2 are structurally closely related to the semicorrins 1. Removal of a proton at the methylene bridge leads to anionic ligands which provide essentially the same steric environment for a coordinated metal ion as the corresponding semicorrinates (cf. 3). Chiral tetrahydrobis[oxazoles] of this type can be easily synthesized from amino alcohols and malonic acid. Starting from other dicarboxylic

The life cycle of Ectocarpus siliculosus from Naples (Italy) was investigated, using well defined cultured material. Gametophytes and sporophytes differ morphologically and functionally. The gametophytes are dioecious, with genotypic determination of their sex. Sporophytes exist in the haploid, diploid and tetraploid phase. All sporophytes can form unilocular sporangia. In tetraploid and diploid sporophytes the formation of unilocular sporangia is connected with meiosis. Certain motile cells of haploid plants may spontaneously give rise to diploid or tetraploid sporophytes which are homozygous. Gametophytes can only be formed together with sporophytes form the swarmers of unilocular sporangia (heteroblasty). Meiosis in tetraploid sporophytes resulted in diploid gametophytes, the gametes of which fused with haploid female gametes. All observed nuclear phases and growth forms are connected with each other by meiosis, heteroblasty, fusion of gametes and spontaneous increase in chromosome number.

The phylogeny of Ectocarpus and Kuckuckia strains representing widely separated populations ?om both hemispheres was infmed from sequence analysis of the internal transcribed spacers of the nuclear ribosomal DNA (ITS 1-5.8s-ITS 2) and Lhe spucer regton i n the plastid-encoded ribulos~bis-phosphate-carboxylase (RUBISCO) cistron (partial rbc L-spac:er+artial rbcS) . Both sequences resulted in matching phylogenies, with the RUBISCO spacer regzon being most i r~o~a t i v~ at the h e 1 of genera and .specie.s and the i n t m a l transm'bed spacer sequences at the level of species and populations. Three major clades were -formed f q strains previously described morphology and physiolob us Kuckuckia, E. fasciculatus, and E. siliculosus, con$min,g the validity of the.w taxa. Ectocarpus and Kuckuckia are regarded as sibling taxa with respect to the outgroup .species Feldmannia simplex, Hincksia mitchelliae, and Pilayella littoralis. The clade f m e d by .sexual E. siliculosus .strains and most asexual Ectocarpus strains was subdivided into several clades that are consistent with geographical races within E. siliculosus. The inferred phylogeny of Ectocarpus corresponds generally with resu1t.r from cro.ss-f)rrilization expm'ment.s, mmphology, and lipid analysis. A hypothesis on the origzn and dispersal of E. siliculosus suggests several natural dispersal events during periods of global cooling as well as recent and po.rsibly anthropogenic dispmsal event.$.

The Ectocarpus siliculosus Virus-1, EsV-1, is the type-species of a genus of Phycodnaviridae, the phaeoviruses, infecting marine filamentous brown algae. The EsV-1 genome of 335,593 bp contains tandem and dispersed repetitive elements in addition to a large number of open reading frames of which 231 are currently counted as genes. Many genes can be assigned to functional groups involved in DNA synthesis, DNA integration, transposition, and polysaccharide metabolism. Furthermore, EsV-1 contains components of a surprisingly complex signal transduction system with six different hybrid histidine protein kinases and four putative serine/threonine protein kinases. Several other genes encode polypeptides with protein-protein interaction domains. However, 50% of the predicted genes have no counterparts in data banks. Only 28 of the 231 identified genes have significant sequence similarities to genes of the Chlorella virus PBCV-1, another phycodnavirus. To our knowledge, the EsV-1 genome is the largest viral DNA sequenced to date.