Schizosaccharomyces pombe contains a single gene, rasi, which is a homolog of the mammalian RAS genes.rasl is required for conjugation, sporulation, and normal cell shape. rasi has been previously identified as steS.We report here a gene we call byr2 that can encode a predicted protein kinase and can partially suppress defects in rasi mutants. rasi mutant strains expressing high levels of byr2 can sporulate competently but are still defective in conjugation and abnormally round. byr2 mutants are viable and have normal shape but are absolutely defective in conjugation and sporulation. byr2 is probably identical to ste8. In many respects, byr2 resembles the byrl gene, another suppressor of the rasi mutation, which has been identified previously as stel. Our data indicate that if rasi, byr2, and byri act along the same pathway, then the site of action for byr2 is between the sites for rasi and byrl.RAS proteins are ubiquitous in evolution. They are lowmolecular-weight guanine nucleotide-binding proteins that function in signal transduction pathways (1). Mutant activated RAS genes are found in a large number of mammalian tumors, but despite their importance, their function in mammals is unknown. We have studied RAS in the yeast Saccharomyces cerevisiae, in which two RAS proteins, RAS1 and RAS2, regulate the function of adenylyl cyclase (23). The latter does not appear to be the function of RAS in vertebrates or even in the fission yeast Schizosaccharomyces pombe (7,20). We have therefore begun to study RAS function in S. pombe in the hope of learning whether there are general principles which govern the functions of RAS proteins in cells.S. pombe contains a single RAS gene, rasl (6, 21). rasi is not an essential gene but functions in the sexual differentiation pathways of that yeast (7,20). rasl mutant cells fail to conjugate and to sporulate. Such cells are also round, unlike wild-type cells, which are elongated. S. pombe cells that contain the activated mutant rasJVal17 allele are also partially sterile. Such cells enter the early phase of conjugation and develop elongated conjugation tubes but fail to enter the subsequent phases.In S. pombe, there are two mating types, designated h+ and h-(4). Only opposite mating types conjugate, and only upon starvation. Homothallic (h90) haploid strains regularly switch mating type and therefore self-mate. Heterothallic (h+ and h-) strains do not switch mating type and do not self-mate. Conjugation can be divided into an early phase, marked by an increase in cell agglutination and the formation of a conjugation tube, and a later phase, marked by the fusion of cells and karyogamy. Immediately following conjugation, most cells undergo zygotic sporulation. Diploid cells, formed either by mating or by other means, can be propagated stably, but diploid strains containing both mating type loci will undergo azygotic sporulation upon starvation. The four-spored asci formed by zygotic sporulation look different from the four-spored asci formed by azygotic * Corresponding author. sporul...

CYP51 (Erg11) belongs to the cytochrome P450 monooxygenase (CYP) superfamily and mediates a crucial step of the synthesis of ergosterol, which is a fungal-specific sterol. It is also the target of azole drugs in clinical practice. In recent years, researches on fungal CYP51 have stepped into a new stage attributing to the discovery of crystal structures of the homologs in Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus . This review summarizes the functions, structures of fungal CYP51 proteins, and the inhibitors targeting these homologs. In particular, several drug-resistant mechanisms associated with the fungal CYP51s are introduced. The sequences and crystal structures of CYP51 proteins in different fungal species are also compared. These will provide new insights for the advancement of research on antifungal agents.

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Flavonols are produced by the desaturation of dihydroflavanols, which is catalyzed by flavonol synthase (FLS). FLS belongs to the 2-oxoglutarate iron-dependent oxygenase family. The full-length cDNA and genomic DNA sequences of the FLS gene (designated as GbFLS) were isolated from Ginkgo biloba. The full-length cDNA of GbFLS contained a 1023-bp open reading frame encoding a 340-amino-acid protein. The GbFLS genomic DNA had three exons and two introns. The deduced GbFLS protein showed high identities with other plant FLSs. The conserved amino acids (H-X-D) ligating ferrous iron and residues (R-X-S) participating in 2-oxoglutarate binding were found in GbFLS at similar positions like other FLSs. GbFLS was found to be expressed in all tested tissues including roots, stems, leaves, and fruits. Expression profiling analyses revealed that GbFLS expression was induced by all of the six tested abiotic stresses, namely, UV-B, abscisic acid, cold, sucrose, salicylic acid, and ethephon, consistent with the in silico analysis results of the promoter region. The recombinant protein was successfully expressed in the E. coli strain BL21 (DE3) with a pET-28a vector. The in vitro enzyme activity assay by high performance liquid chromatography indicated that recombinant GbFLS protein could catalyze the formation of dihydrokaempferol to kaempferol and the conversion of kaempferol from naringenin, suggesting that GbFLS is a bifunctional enzyme within the flavonol biosynthetic pathway.

Shigella flexneri is the major pathogen causing bacillary dysentery in developing countries. S. flexneri is divided into at least 16 serotypes based on the combination of antigenic determinants present in the O-antigen. All the serotypes (except for serotype 6) share a basic O-unit containing one N-acetyl-d-glucosamine and three l-rhamnose residues, whereas differences between the serotypes are conferred by phage-encoded glucosylation and/or O-acetylation. Serotype Xv is a newly emerged and the most prevalent serotype in China, which can agglutinate with both MASF IV-1 and 7,8 monoclonal antibodies. The factor responsible for the presence of MASF IV-1 (E1037) epitope has not yet been identified. In this study, we analyzed the LPS structure of serotype Xv strains and found that the MASF IV-1 positive phenotype depends on an O-antigen modification with a phosphoethanolamine (PEtN) group attached at position 3 of one of the rhamnose residues. A plasmid carried gene, lpt-O (LPS phosphoethanolamine transferase for O–antigen), mediates the addition of PEtN for serotype Xv and other MASF IV-1 positive strains. These findings reveal a novel serotype conversion mechanism in S. flexneri and show the necessity of further extension of the serotype classification scheme recognizing the MASF IV-1 positive strains as distinctive subtypes.