No abstract

A practical and general Reformatsky reaction, promoted by oxidants and mediated by dimethylzinc, is described. The reaction is fast and runs at 0 °C with aldehydes and ketones, under mild reaction conditions. Preliminary results obtained for the enantioselective version show that inexpensive chiral amino alcohols could be used in the challenging formation of enantioenriched quaternary stereogenic centers.

Over-expression of the yeast PEP4 gene encoding the vacuolar aspartic protease proteinase A (PrA) leads to saturation of the vacuolar targeting system of the cell and missorting of PrA to the growth medium. In a screen for genes affecting the secretion of over-expressed PrA we found that multiple copies of the open reading frame (ORF) YAL048c enhanced PrA secretion. Since no function has hitherto been ascribed to YAL048c, we undertook further studies of this ORF. Deletion of YAL048c resulted in slightly reduced secretion of over-produced PrA. Furthermore, strains deleted for YAL048c showed a growth inhibition phenotype resulting in wrinkled colony morphology when grown on rich medium containing high concentrations of calcium. YAL048c is predicted to encode a polypeptide of 662 amino acid residues containing two consensus ATP/GTP-binding site motifs and a putative carboxy-terminal transmembrane region. In addition, the amino acid sequence contains two putative calcium-binding domains. The YAL048c protein may be evolutionarily conserved, as homologues exist in humans and Caenorhabditis elegans. We suggest that the YAL048c protein is involved in vesicle transport in the secretory pathway.

Transformation of Mucor circinelloides is routinely achieved by using a plasmid containing the wild-type leuA gene to complement the leucine requirement of an auxotrophic host strain. As is the case for other zygomycetes, the transforming DNA is usually not integrated into the genome of M. circinelloides, but is maintained as an autonomously replicating plasmid. However, even under selective conditions, the plasmid is segregationally unstable, resulting in a rather low number of cells carrying the plasmid. We report here on a new transformation vector based on a dominant selection marker conferring resistance to geneticin, which allows for plasmid maintenance in high copy numbers. The vector was also used to transform Mucor rouxii and Rhizomucor pusillus, and should therefore be a valuable tool for gene expression studies in zygomycetes. The functionality and regulatory properties of the promoter of the M. circinelloides gpd1 gene (which codes for glyceraldehyde-3P-dehydrogenase) were demonstrated in R. pusillus using geneticin selection. In this work, we have also determined the molecular basis of the Leu(-) phenotype of the M. circinelloides host strain R7B. The leucine requirement is due to a single point mutation in the leuA gene that results in the replacement of a glutamic acid by a lysine residue.

Mucor circinelloides (syn. racemosus) is a non-pathogenic dimorphic fungus belonging to the class of zygomycetes. We are developing a novel system for heterologous protein production exploiting the dimorphic growth characteristics of M. circinelloides. In order to identify potential genetic regulators of morphology we have initiated a characterisation of key genes involved in signal transduction in Mucor. We have cloned and characterised pkaR and pkaC encoding the regulatory subunit (PKAR) and the catalytic subunit (PKAC), respectively, of the cAMP-dependent protein kinase A (PKA) of M. circinelloides. In anaerobically grown yeast cells, the levels of expression of both pkaR and pkaC were significantly higher than the levels of expression in aerobically grown mycelium. However, during the dimorphic shift, i.e. during the transition from anaerobic yeast growth to aerobic filamentous growth, the expression of pkaR was found to increase approximately two-fold. These results indicate that regulation of PKA activity is conferred at different levels according to growth and environmental conditions. Overexpression of pkaR resulted in a multi-branched colony phenotype on solid medium indicating that PKAR plays a role in filamentation and branching. Fragments of genes encoding factors of the mitogen-activated protein (MAP) kinase (MAPK) pathway have also been cloned: mpk1 (mitogen-activated protein kinase 1) encoding a MAPK homologue and ste12 encoding a transcription factor.