scholarly journals A role for CDC7 in repression of transcription at the silent mating-type locus HMR in Saccharomyces cerevisiae.

1991 ◽  
Vol 11 (2) ◽  
pp. 1080-1091 ◽  
Author(s):  
A Axelrod ◽  
J Rine
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Binding Site ◽  
Mating Type ◽  
Double Mutant ◽  
Temperature Sensitive ◽  
Alpha Cells ◽  
Nucleotide Substitutions ◽  
Type Locus

The mating-type genes at MAT in Saccharomyces cerevisiae are expressed, whereas the same genes located at HML and HMR are transcriptionally repressed. The DNA element responsible for repression at HMR has been termed a silencer and contains an autonomous replication sequence, a binding site for GRFI/RAPI, and a binding site for ABFI. A double-mutant HMR-E silencer that contains single nucleotide substitutions in both the GRFI/RAPI- and ABFI-binding sites no longer binds either factor in vitro, nor represses transcription at HMR in vivo. In MAT alpha cells, this derepression of a information results in a nonmating phenotype. Second-site suppressor mutations were isolated that restored the alpha mating phenotype to MAT alpha cells containing the double-mutant silencer. One of these suppressors, designated sas1-1, conferred a temperature-sensitive lethal phenotype to the cell. SAS1 was found to be identical to CDC7, a gene which encodes a protein kinase required for the initiation of DNA replication. This new allele of CDC7 was designated cdc7-90. cdc7-90 restored the alpha mating phenotype by restoring silencing. The original allele of CDC7, isolated on the basis of the cell cycle phenotype it confers, also restored silencing, and overexpression of CDC7 interfered with silencing. cdc7-90 did not restore detectable binding of GRFI/RAPI or ABFI to the double-mutant silencer in vitro. These results indicate that a reduced level of CDC7 function restores silencing to a locus defective in binding two factors normally required for silencing.

A role for CDC7 in repression of transcription at the silent mating-type locus HMR in Saccharomyces cerevisiae

1991 ◽  
Vol 11 (2) ◽  
pp. 1080-1091
Author(s):  
A Axelrod ◽  
J Rine
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Binding Site ◽  
Mating Type ◽  
Double Mutant ◽  
Temperature Sensitive ◽  
Alpha Cells ◽  
Nucleotide Substitutions ◽  
Type Locus

The mating-type genes at MAT in Saccharomyces cerevisiae are expressed, whereas the same genes located at HML and HMR are transcriptionally repressed. The DNA element responsible for repression at HMR has been termed a silencer and contains an autonomous replication sequence, a binding site for GRFI/RAPI, and a binding site for ABFI. A double-mutant HMR-E silencer that contains single nucleotide substitutions in both the GRFI/RAPI- and ABFI-binding sites no longer binds either factor in vitro, nor represses transcription at HMR in vivo. In MAT alpha cells, this derepression of a information results in a nonmating phenotype. Second-site suppressor mutations were isolated that restored the alpha mating phenotype to MAT alpha cells containing the double-mutant silencer. One of these suppressors, designated sas1-1, conferred a temperature-sensitive lethal phenotype to the cell. SAS1 was found to be identical to CDC7, a gene which encodes a protein kinase required for the initiation of DNA replication. This new allele of CDC7 was designated cdc7-90. cdc7-90 restored the alpha mating phenotype by restoring silencing. The original allele of CDC7, isolated on the basis of the cell cycle phenotype it confers, also restored silencing, and overexpression of CDC7 interfered with silencing. cdc7-90 did not restore detectable binding of GRFI/RAPI or ABFI to the double-mutant silencer in vitro. These results indicate that a reduced level of CDC7 function restores silencing to a locus defective in binding two factors normally required for silencing.

scholarly journals Transcription of alpha-specific genes in Saccharomyces cerevisiae: DNA sequence requirements for activity of the coregulator alpha 1.

1993 ◽  
Vol 13 (11) ◽  
pp. 6866-6875 ◽  
Author(s):  
D C Hagen ◽  
L Bruhn ◽  
C A Westby ◽  
G F Sprague
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Binding Site ◽  
Dna Sequences ◽  
Point Mutations ◽  
Transcription Activation ◽  
Specific Gene ◽  
Binding Assays ◽  
Weak Binding

Transcription activation of alpha-specific genes in Saccharomyces cerevisiae is regulated by two proteins, MCM1 and alpha 1, which bind to DNA sequences, called P'Q elements, found upstream of alpha-specific genes. Neither MCM1 nor alpha 1 alone binds efficiently to P'Q elements. Together, however, they bind cooperatively in a manner that requires both the P' sequence, which is a weak binding site for MCM1, and the Q sequence, which has been postulated to be the binding site for alpha 1. We analyzed a collection of point mutations in the P'Q element of the STE3 gene to determine the importance of individual base pairs for alpha-specific gene transcription. Within the 10-bp conserved Q sequence, mutations at only three positions strongly affected transcription activation in vivo. These same mutations did not affect the weak binding to P'Q displayed by MCM1 alone. In vitro DNA binding assays showed a direct correlation between the ability of the mutant sequences to form ternary P'Q-MCM1-alpha 1 complexes and the degree to which transcription was activated in vivo. Thus, the ability of alpha 1 and MCM1 to bind cooperatively to P'Q elements is critical for activation of alpha-specific genes. In all natural alpha-specific genes the Q sequence is adjacent to the degenerate side of P'. To test the significance of this geometry, we created several novel juxtapositions of P, P', and Q sequences. When the Q sequence was opposite the degenerate side, the composite QP' element was inactive as a promoter element in vivo and unable to form stable ternary QP'-MCM1-alpha 1 complexes in vitro. We also found that addition of a Q sequence to a strong MCM1 binding site allows the addition of alpha 1 to the complex. This finding, together with the observation that Q-element point mutations affected ternary complex formation but not the weak binding of MCM1 alone, supports the idea that the Q sequence serves as a binding site for alpha 1.

Functional interaction between p21rap1A and components of the budding pathway in Saccharomyces cerevisiae

1992 ◽  
Vol 12 (9) ◽  
pp. 4084-4092
Author(s):  
P C McCabe ◽  
H Haubruck ◽  
P Polakis ◽  
F McCormick ◽  
M A Innis
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mammalian Cells ◽  
Bound States ◽  
Yeast Cells ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Amino Terminal ◽  
Loop Region

The rap1A gene encodes a 21-kDa, ras-related GTP-binding protein (p21rap1A) of unknown function. A close structural homolog of p21rap1A (65% identity in the amino-terminal two-thirds) is the RSR1 gene product (Rsr1p) of Saccharomyces cerevisiae. Although Rsr1p is not essential for growth, its presence is required for nonrandom selection of bud sites. To assess the similarity of these proteins at the functional level, wild-type and mutant forms of p21rap1A were tested for complementation of activities known to be fulfilled by Rsr1p. Expression of p21rap1A, like multicopy expression of RSR1, suppressed the conditional lethality of a temperature-sensitive cdc24 mutation. Point mutations predicted to affect the localization of p21rap1A or its ability to cycle between GDP and GTP-bound states disrupted suppression of cdc24ts, while other mutations in the 61-65 loop region improved suppression. Expression of p21rap1A could not, however, suppress the random budding phenotype of rsr1 cells. p21rap1A also apparently interfered with the normal activity of Rsrlp, causing random budding in diploid wild-type cells, suggesting an inability of p21rap1A to interact appropriately with Rsr1p regulatory proteins. Consistent with this hypothesis, we found an Rsr1p-specific GTPase-activating protein (GAP) activity in yeast membranes which was not active toward p21rap1A, indicating that p21rap1A may be predominantly GTP bound in yeast cells. Coexpression of human Rap1-specific GAP suppressed the random budding due to expression of p21rap1A or its derivatives, including Rap1AVal-12. Although Rap1-specific GAP stimulated the GTPase of Rsr1p in vitro, it did not dominantly interfere with Rsr1p function in vivo. A chimera consisting of Rap1A1-165::Rsr1p166-272 did not exhibit normal Rsr1p function in the budding pathway. These results indicated that p21rap1A and Rsr1p share at least partial functional homology, which may have implications for p21rap1A function in mammalian cells.

scholarly journals Translation initiation factor 4A from Saccharomyces cerevisiae: analysis of residues conserved in the D-E-A-D family of RNA helicases.

1991 ◽  
Vol 11 (7) ◽  
pp. 3463-3471 ◽  
Author(s):  
S R Schmid ◽  
P Linder
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Translation Initiation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Clear Correlation ◽  
Temperature Sensitive ◽  
Rna Helicases ◽  
Initiation Of Translation

The eukaryotic translation initiation factor 4A (eIF-4A) possesses an in vitro helicase activity that allows the unwinding of double-stranded RNA. This activity is dependent on ATP hydrolysis and the presence of another translation initiation factor, eIF-4B. These two initiation factors are thought to unwind mRNA secondary structures in preparation for ribosome binding and initiation of translation. To further characterize the function of eIF-4A in cellular translation and its interaction with other elements of the translation machinery, we have isolated mutations in the TIF1 and TIF2 genes encoding eIF-4A in Saccharomyces cerevisiae. We show that three highly conserved domains of the D-E-A-D protein family, encoding eIF-4A and other RNA helicases, are essential for protein function. Only in rare cases could we make a conservative substitution without affecting cell growth. The mutants show a clear correlation between their growth and in vivo translation rates. One mutation that results in a temperature-sensitive phenotype reveals an immediate decrease in translation activity following a shift to the nonpermissive temperature. These in vivo results confirm previous in vitro data demonstrating an absolute dependence of translation on the TIF1 and TIF2 gene products.

Functional conservation of tRNase ZL among Saccharomyces cerevisiae, Schizosaccharomyces pombe and humans

2009 ◽  
Vol 422 (3) ◽  
pp. 483-492 ◽  
Author(s):  
Zhen Zhao ◽  
Wenchen Su ◽  
Sheng Yuan ◽  
Ying Huang
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Schizosaccharomyces Pombe ◽  
Cancer Susceptibility ◽  
Short Form ◽  
Susceptibility Gene ◽  
Temperature Sensitive ◽  
Functional Conservation ◽  
Trnase Z

Although tRNase Z from various organisms was shown to process nuclear tRNA 3′ ends in vitro, only a very limited number of studies have reported its in vivo biological functions. tRNase Z is present in a short form, tRNase ZS, and a long form, tRNase ZL. Unlike Saccharomyces cerevisiae, which contains one tRNase ZL gene (scTRZ1) and humans, which contain one tRNase ZL encoded by the prostate-cancer susceptibility gene ELAC2 and one tRNase ZS, Schizosaccharomyces pombe contains two tRNase ZL genes, designated sptrz1+ and sptrz2+. We report that both sptrz1+ and sptrz2+ are essential for growth. Moreover, sptrz1+ is required for cell viability in the absence of Sla1p, which is thought to be required for endonuclease-mediated maturation of pre-tRNA 3′ ends in yeast. Both scTRZ1 and ELAC2 can complement a temperature-sensitive allele of sptrz1+, sptrz1–1, but not the sptrz1 null mutant, indicating that despite exhibiting species specificity, tRNase ZLs are functionally conserved among S. cerevisiae, S. pombe and humans. Overexpression of sptrz1+, scTRZ1 and ELAC2 can increase suppression of the UGA nonsense mutation ade6–704 through facilitating 3′ end processing of the defective suppressor tRNA that mediates suppression. Our findings reveal that 3′ end processing is a limiting step for defective tRNA maturation and demonstrate that overexpression of sptrz1+, scTRZ1 and ELAC2 can promote defective tRNA 3′ processing in vivo. Our results also support the notion that yeast tRNase ZL is absolutely required for 3′ end processing of at least a few pre-tRNAs even in the absence of Sla1p.

scholarly journals Impact of Mating Type, Serotype, and Ploidy on the Virulence of Cryptococcus neoformans

2008 ◽  
Vol 76 (7) ◽  
pp. 2923-2938 ◽  
Author(s):  
Xiaorong Lin ◽  
Kirsten Nielsen ◽  
Sweta Patel ◽  
Joseph Heitman
Keyword(s):  
Cryptococcus Neoformans ◽  
Mating Type ◽  
Pathogenic Fungi ◽  
Mating Types ◽  
Type Locus ◽  
Virulence Potential ◽  
The Impact ◽  
Ad Hybrids

ABSTRACT Hybridization with polyploidization is a significant biological force driving evolution. The effect of combining two distinct genomes in one organism on the virulence potential of pathogenic fungi is not clear. Cryptococcus neoformans, the most common cause of fungal infection of the central nervous system, has a bipolar mating system with a and α mating types and occurs as A (haploid), D (haploid), and AD hybrid (mostly diploid) serotypes. Diploid AD hybrids are derived either from a-α mating or from unisexual mating between haploid cells. The precise contributions of increased ploidy, the effect of hybridization between serotypes A and D, and the combination of mating types to the virulence potential of AD hybrids have remained elusive. By using in vitro and in vivo characterization of laboratory-constructed isogenic diploids and AD hybrids with all possible mating type combinations in defined genetic backgrounds, we found that higher ploidy has a minor negative effect on virulence in a murine inhalation model of cryptococcosis. The presence of both mating types a and α in AD hybrids did not affect the virulence potential, irrespective of the serotype origin. Interestingly, AD hybrids with only one mating type behaved differently, with the virulence of αADα strains similar to that of other hybrids, while aADa hybrids displayed significantly lower virulence due to negative epistatic interactions between the Aa and Da alleles of the mating type locus. This study provides insights into the impact of ploidy, mating type, and serotype on virulence and the impact of hybridization on the fitness and virulence of a eukaryotic microbial pathogen.

scholarly journals In vivo analysis of the Saccharomyces cerevisiae HO nuclease recognition site by site-directed mutagenesis.

1990 ◽  
Vol 10 (3) ◽  
pp. 1174-1179 ◽  
Author(s):  
J A Nickoloff ◽  
J D Singer ◽  
F Heffron
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mating Type ◽  
Shuttle Vector ◽  
Strand Break ◽  
Recognition Site ◽  
Site Directed Mutagenesis ◽  
Type Locus ◽  
Intact Core ◽  
Site Recognition

HO nuclease introduces a specific double-strand break in the mating-type locus (MAT) of Saccharomyces cerevisiae, initiating mating-type interconversion. To define the sequence recognized by HO nuclease, random mutations were produced in a 30-base-pair region homologous to either MAT alpha or MATa by a chemical synthesis procedure. The mutant sites were introduced into S. cerevisiae on a shuttle vector and tested for the ability to stimulate recombination in an assay that mimics mating-type interconversion. The results suggest that a core of 8 noncontiguous bases near the Y-Z junction of MAT is essential for HO nuclease to bind and cleave its recognition site. Other contacts must be required because substrates that contain several mutations outside an intact core reduce or eliminate cleavage in vivo. The results show that HO site recognition is a complex phenomenon, similar to promoter-polymerase interactions.

scholarly journals p62cdc23 of Saccharomyces cerevisiae: a nuclear tetratricopeptide repeat protein with two mutable domains.

1993 ◽  
Vol 13 (2) ◽  
pp. 1212-1221 ◽  
Author(s):  
R S Sikorski ◽  
W A Michaud ◽  
P Hieter
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle Progression ◽  
Single Amino Acid ◽  
Temperature Sensitive ◽  
Cycle Progression ◽  
Tetratricopeptide Repeats ◽  
Tetratricopeptide Repeat Protein ◽  
Cdc Genes

CDC23 is required in Saccharomyces cerevisiae for cell cycle progression through the G2/M transition. The CDC23 gene product contains tandem, imperfect repeats, termed tetratricopeptide repeats, (TPR) units common to a protein family that includes several other nuclear division CDC genes. In this report we have used mutagenesis to probe the functional significance of the TPR units within CDC23. Analysis of truncated derivatives indicates that the TPR block of CDC23 is necessary for the function or stability of the polypeptide. In-frame deletion of a single TPR unit within the repeat block proved sufficient to inactivate CDC23 in vivo, though this allele could rescue the temperature-sensitive defect of a cdc23 point mutant by intragenic complementation. By both in vitro and in vivo mutagenesis techniques, 17 thermolabile cdc23 alleles were produced and examined. Fourteen alleles contained single amino acid changes that were found to cluster within two distinct mutable domains, one of which encompasses the most canonical TPR unit found in CDC23. In addition, we have characterized CDC23 as a 62-kDa protein (p62cdc23) that is localized to the yeast nucleus. Our mutagenesis results suggest that TPR blocks form an essential domain within members of the TPR family.

scholarly journals Processivity of the Saccharomyces cerevisiae Poly(A) Polymerase Requires Interactions at the Carboxyl-Terminal RNA Binding Domain

1998 ◽  
Vol 18 (10) ◽  
pp. 5942-5951 ◽  
Author(s):  
Alexander Zhelkovsky ◽  
Steffen Helmling ◽  
Claire Moore
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Binding Site ◽  
Rna Binding ◽  
Atp Binding Site ◽  
Nucleotide Binding Sites ◽  
Carboxyl Terminal ◽  
Unique Specificity ◽  
Carboxy Terminal

ABSTRACT The interaction of the Fip1 subunit of polyadenylation factor I with the Saccharomyces cerevisiae poly(A) polymerase (PAP) was assayed in vivo by two-hybrid analysis and was found to involve two separate regions on PAP, located at opposite ends of the protein sequence. In vitro, Fip1 blocks access of the RNA primer to an RNA binding site (RBS) that overlaps the Fip1 carboxy-terminal interaction region and, in doing so, shifts PAP to a distributive mode of action. Partial truncation of this RBS has the same effect, indicating that this site is required for processivity. A comparison of the utilization of ribo- and deoxyribonucleotides as substrates indicates the existence on PAP of a second RBS which recognizes the last three nucleotides at the 3′ end of the primer. This site discriminates against deoxyribonucleotides at the 3′ end, and interactions at this site are not affected by Fip1. Further analysis revealed that the specificity of PAP for adenosine is not simply a function of the ATP binding site but also reflects interactions with bases at the 3′ end of the primer and at another contact site 14 nucleotides upstream of the 3′ end. These results suggest that the unique specificity of PAP for ribose and base, and thus the extent and type of activity with different substrates, depends on interactions at multiple nucleotide binding sites.

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