A 21.7 kb DNA segment on the left arm of yeast chromosome XIV carries WHI3, GCR2, SPX18, SPX19, an homologue to the heat shock gene SSB1 and 8 new open reading frames of unknown function

Screening for new yeast mutants affected in mannosylphosphorylation of cell wall mannoproteins

We have carried out a screen of 622 deletion strains generated during the EUROFAN B0 project to identify non-essential genes related to the mannosylphosphate content of the cell wall. By examining the affinity of the deletants for the cationic dye alcian blue and the ion exchanger QAE-Sephadex, we have selected 50 strains. On the basis on their reactivity (blue colour intensity) in the alcian blue assay, mutants with a lower phosphate content than wild-type cells were then arranged in groups defined by previously characterized mutants, as follows: group I (mnn6), group II (between mnn6 and mnn9) and group III (mnn9). Similarly, strains that behaved like mnn1 (i.e. a blue colour deeper than wild-type) were included in group VI. To confirm the association between the phenotype and a specific mutation, strains were complemented with clones or subjected to tetrad analysis. Selected strains were further tested for extracellular invertase and exoglucanase. Within groups I, II and III, we found some genes known to be involved in oligosaccharide biosynthesis (ALG9, ALG12, HOC1), secretion (BRE5, COD4/COG5, VPS53), transcription (YOL072w/THP1, ELP2, STB1, SNF11), cell polarity (SEP7, RDG1), mitochondrial function (YFH1), cell metabolism, as well as orphan genes. Within group VI, we found genes involved in environmentally regulated transduction pathways (PAL2 and RIM20) as well as others with miscellaneous or unknown functions. We conclude that mannosylphosphorylation is severely impaired in some deletants deficient in specific glycosylation/secretion processes, but many other different pathways may also modulate the amount of mannosylphosphate in the cell wall.

Molecular characterization of genes encoding cytosolic Hsp70s in the zygomycete fungus Rhizopus nigricans

Previous studies have shown that some stressors, including steroid hormones 21-OH progesterone and testosterone, stimulate the accumulation of heat shock protein 70 (hsp70) messenger ribonucleic acid (mRNA) population in the zygomycete filamentous fungus Rhizopus nigricans. In this study we report the cloning of 3 R nigricans hsp70 genes (Rnhsp70-1, Rnhsp70-2, and Rnhsp70-3) encoding cytosolic Hsp70s. With a Southern blot experiment under high stringency conditions we did not detect any additional highly homologous copies of the cytosolic hsp70 genes in the R nigricans genome. Sequence analyses showed that all 3 genes contain introns within the open reading frame. The dynamics of the R nigricans molecular response to progesterone, 21-OH progesterone, and testosterone, as well as to heat shock, copper ions, hydrogen peroxide, and ethanol was studied by temporal analysis of Rnhsp70-1 and Rnhsp70-2 mRNA accumulation. Northern blot experiments revealed that the Rnhsp70-2 transcript level is not affected by testosterone, whereas mRNA levels of both genes are rapidly increased with all the other stressors studied. Moreover, the decrease of transcript levels is notably delayed in ethanol stress, and a difference is observed between the profiles of Rnhsp70-1 and Rnhsp70-2 transcripts during heat stress.

Multiple regulators of Ty1 transposition in Saccharomyces cerevisiae have conserved roles in genome maintenance

Most Ty1 retrotransposons in the genome of Saccharomyces cerevisiae are transpositionally competent but rarely transpose. We screened yeast mutagenized by insertion of the mTn3-lacZ/LEU2 transposon for mutations that result in elevated Ty1 cDNA-mediated mobility, which occurs by cDNA integration or recombination. Here, we describe the characterization of mTn3 insertions in 21 RTT (regulation of Ty1 transposition) genes that result in 5- to 111-fold increases in Ty1 mobility. These 21 RTT genes are EST2, RRM3, NUT2, RAD57, RRD2, RAD50, SGS1, TEL1, SAE2, MED1, MRE11, SCH9, KAP122, and 8 previously uncharacterized genes. Disruption of RTT genes did not significantly increase Ty1 RNA levels but did enhance Ty1 cDNA levels, suggesting that most RTT gene products act at a step after mRNA accumulation but before cDNA integration. The rtt mutations had widely varying effects on integration of Ty1 at preferred target sites. Mutations in RTT101 and NUT2 dramatically stimulated Ty1 integration upstream of tRNA genes. In contrast, a mutation in RRM3 increased Ty1 mobility >100-fold without increasing integration upstream of tRNA genes. The regulation of Ty1 transposition by components of fundamental pathways required for genome maintenance suggests that Ty1 and yeast have coevolved to link transpositional dormancy to the integrity of the genome.

The HMG protein T160 colocalizes with DNA replication foci and is down-regulated during cell differentiation

The high mobility group protein T160, the murine homolog of the human structure-specific recognition protein 1, was first supposed to be involved in the process of V-(D)-J recombination, since it could bind to recombination signal sequence probes. We have recently cloned T160 by using an unrelated DNA probe and shown that it binds to either cruciform or linear DNA with no sequence specificity. In this work, we performed a detailed analysis of T160 expression and immunolocalization. We show that T160 is a phosphoprotein broadly conserved from yeast to mammals, with a high level of expression in all the cell lines tested and in tissues containing a high degree of proliferating cells. Indirect immunofluorescence analysis by confocal laser microscopy revealed that T160 distribution in the cell nucleus is not uniform, and focus-like staining was observed. Cell cycle studies by BrdU incorporation suggest that the appearance of T160 nuclear foci is specific of mid to late S phase. Furthermore, while T160 expression does not change during the cell cycle, it is dramatically down-regulated when cells begin to differentiate, as highlighted in C2C12 myoblasts and myotubes. The disappearance of T160 nuclear staining in multinucleated myotubes is shown. Taken together, these data suggest that its function may be less specific than V-(D)-J recombination and more related to some cellular basic process, such as DNA replication or repair.

Cloning of the multicopy suppressor gene SUR7: evidence for a functional relationship between the yeast actin-binding protein Rvs167 and a putative membranous protein

The rvs161 and rvs167 mutant cells exhibit several identical phenotypes including sensitivity to several different growth conditions and morphological defects such as alteration of the actin cytoskeleton and budding patterns. The selection of genes that, when overexpressed, are able to suppress the reduced viability upon carbon starvation of the rvs167 mutant strain, has allowed the cloning of the SUR7 gene (Accession Number Z46729x11). We showed that the suppressive ability of the overexpressed SUR7 gene concerns all the rvs167 phenotypes. However, this suppression is only partial since the rvs167-suppressed strain is not of wild-type phenotype. Moreover, SUR7 is also able to suppress partially the phenotypes exhibited by the rvs161 and rvs167 and rvs161 mutant strains. The SUR7 gene encodes a putative integral membrane protein with four transmembrane domains. Furthermore, sequence comparisons revealed that Sur7p and two other proteins, Yn1194p and Yd1222p, present significant sequence and structural similarities. Taken together, these results strongly suggest that the Rvs161 and Rvs167 proteins act together in relation with Sur7p. Moreover, the putative transmembranous character of Sur7p suggests a membrane localization of the Rvs function, a localization which is consistent with the different rvs phenotypes and the actin-Rvs167p interaction.

Enoyl-acyl-carrier-protein reductase and Mycobacterium tuberculosis InhA do not conserve the Tyr-Xaa-Xaa-Xaa-Lys motif in mammalian 11 beta- and 17 beta-hydroxysteroid dehydrogenases and Drosophila alcohol dehydrogenase

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