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The KRE2/MNT1 mannosyltransferase gene family of Saccharomyces cerevisiae currently consists of the KRE2, YUR1, KTR1, KTR2, KTR3 and KTR4 genes. All six encode putative type II membrane proteins with a short cytoplasmic N-terminus, a membrane-spanning region and a highly conserved catalytic lumenal domain. Here we report the identification of the three remaining members of this family in the yeast genome. KTR5 corresponds to an open reading frame (ORF) of the left arm of chromosome XIV, and KTR6 and KTR7 to ORFs on the left arms of chromosomes XVI and IX respectively. The KTR5, KTR6 and KTR7 gene products are highly similar to the Kre2p/Mnt1p family members. Initial functional characterization revealed that some mutant yeast strains containing null copies of these genes displayed cell wall phenotypes. None was K1 killer toxin resistant but ktr6 and ktr7 null mutants were found to be hypersensitive and resistant, respectively, to the drug Calcofluor White. The sequences have been deposited in the GenBank data library under Accession Numbers Z71305; U39205; Z46728.©1997 John Wiley & Sons, Ltd.

The sequenced yeast genome offers a unique resource for the analysis of eukaryotic cell function and enables genome-wide screens for genes involved in cellular processes. We have identified genes involved in cell surface assembly by screening transposon-mutagenized cells for altered sensitivity to calcofluor white, followed by supplementary screens to further characterize mutant phenotypes. The mutated genes were directly retrieved from genomic DNA and then matched uniquely to a gene in the yeast genome database. Eighty-two genes with apparent perturbation of the cell surface were identified, with mutations in 65 of them displaying at least one further cell surface phenotype in addition to their modified sensitivity to calcofluor. Fifty of these genes were previously known, 17 encoded proteins whose function could be anticipated through sequence homology or previously recognized phenotypes and 15 genes had no previously known phenotype.

In carbonyl compounds RCOX (X = H, Me, SiR3,SR, Cl, F, OMe, OH, NH2, O-; R = H, Me), the O-17 shift values of the carbonyl group depend on the electron donor-acceptor properties of X, whereas the C-13 shift values are determined by other factors too. By IGLO ab initio calculations, the difference between C-13 and O-17 has been traced to differences in the relative importance of the shielding tensor component in the direction of the C-O bond (sigma(zz)). The deshielding contribution of this component is mainly determined by the energy of the n-pi* excitation; donor-acceptor-type interactions influence the level of both orbitals. As the n orbital of this transition is essentially localized on the O atom, the excitation acts less on C-13 and is thus mainly responsible for the difference in substituent sensitivity between C-13 and O-17 shifts. An analogous difference of substituent sensitivities between C-13 and O-17 shifts exists in aroyl compounds p-YC6H4COX towards changes in the para substituent Y; it is explained on the same basis as the effect of X upon RCOX, without the necessity of referring to a 'reverse' substituent effect. Finally, the surprising absence of substituent effects upon the O-17 shift in aroyl cations p-YC6H4CO+ can be explained by the fact that, for symmetry reasons, the n-pi*-type excitation is absent in linear compounds. (C) 1997 by John Wiley & Sons, Ltd

The O-17 NMR signals of trimethylamine oxide and of six (para-substituted) N-aryldimethylamine oxides appear at 240-260 ppm, ca. 200 ppm more deshielded than hydroxylamines. The influence of the arene group and its substituents is small, confirming the absence of resonance interaction between the ring and the N+O- group. X=N+(O-)Ar compounds (X=R(2)C, nitrones; X=RN, azoxy compounds; X=ArN(O), azodioxy compounds = C-nitroso dimers) are more deshielded, delta(0) 350-450 ppm, due to resonance participation of -N=O-type structures (true nitroso compounds X-N=O appear at 650-1500 ppm). Carbonitrile oxides R-C=N+-O- and N=N+-O- show high shielding, delta(0) ca. 140 and 115 ppm, respectively, higher than amine oxides; their C and N atoms also are significantly shielded. The increase in shielding, relative to sp(2)-type pi-systems, is explained by the shielding anisotropy in linear (sp-type) pi-systems. The shirt values observed for four classes of N-O compounds are in excellent agreement with predictions by IGLO calculations