Ribose-5-phosphate isomerase from Saccharomyces cerevisiae: purification and molecular analysis of the enzyme.

Purification and molecular analysis of ribose-5-phosphate isomerase (EC 5.3.1.6) from Saccharomyces cerevisiae is described first time. The enzyme was enriched from a haploid deletion mutant containing the wild-type gene on a multicopy plasmid elaborating the following steps: ammonium sulphate precipitation, interfacial salting out on Sepharose 6B, high performance liquid chromatography on Fractogel EMD DEAE and on Resource Phenyl. The enzyme activity was found to be rather unstable possibly caused by removal of stabilizing cofactors or proteins during the purification procedure. The purified enzyme showed a hyperbolic dependence on the substrate ribose-5-phosphate with a K(m)-value of 1.6 +/- 0.3 mmol/l. For the native enzyme a molecular mass of 115 +/- 10 kDa was determined as found by saccharose density gradient centrifugation, sedimentation equilibrium analysis, size exclusion chromatography and polyacrylamide gel electrophoresis. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and Western blotting revealed one band with a molecular mass of 31 +/- 2 kDa. Thus, the native enzyme is composed of four subunits of identical size. The molecular mass of the subunit and the identified N-terminal sequence of 33 amino acids fits well the 258 amino acid protein encoded by the S. cerevisiae RKI open reading frame, which was characterized previously only by increasing specific activities of ribose-5-phosphate isomerase in cells after cloning the gene. On the basis of the conserved amino acids an alignment of the amino acid sequence of ribose-5-phosphate isomerase from yeast with those of the enzyme from mouse, spinach and Escherichia coli is presented.

Characterization of a glucose-repressed pyruvate kinase (Pyk2p) in Saccharomyces cerevisiae that is catalytically insensitive to fructose-1,6-bisphosphate.

We have characterized the gene YOR347c of Saccharomyces cerevisiae and shown that it encodes a second functional pyruvate kinase isoenzyme, Pyk2p. Overexpression of the YOR347c/PYK2 gene on a multicopy vector restored growth on glucose of a yeast pyruvate kinase 1 (pyk1) mutant strain and could completely substitute for the PYK1-encoded enzymatic activity. PYK2 gene expression is subject to glucose repression. A pyk2 deletion mutant had no obvious growth phenotypes under various conditions, but the growth defects of a pyk1 pyk2 double-deletion strain were even more pronounced than those of a pyk1 single-mutation strain. Pyk2p is active without fructose-1,6-bisphosphate. However, overexpression of PYK2 during growth on ethanol did not cause any of the deleterious effects expected from a futile cycling between pyruvate and phosphoenolpyruvate. The results indicate that the PYK2-encoded pyruvate kinase may be used under conditions of very low glycolytic flux.

Extracellular K+ and Ba2+ mediate voltage-dependent inactivation of the outward-rectifying K+ channel encoded by the yeast gene TOK1.

Gating of the yeast K+ channel encoded by the Saccharomyces cerevisiae gene TOK1, unlike other outward-rectifying K+ channels that have been cloned, is promoted by membrane voltage (inside positive-going) and repressed by extracellular K+. When expressed in Xenopus laevis oocytes, the TOK1p current rectified strongly outward, its activation shifting in parallel with the K+ equilibrium potential when the external K+ concentration ([K+]o) was increased above 3 mM. Analysis of the TOK1p current indicated that two kinetic components contributed to the conductance and the voltage sensitivity of the conductance. By contrast, the [K+]o sensitivity of the current was accommodated entirely within the slow-relaxing component; it was diminished near 1 mM [K+]o, and at submillimolar concentrations the voltage dependence of the TOK1p conductance was insensitive to [K+]o. External Rb+, the K+ channel blockers Cs+ and Ba2+--but not Na+, Ca2+ or Mg2+--substituted for K+ in control of TOK1p activation, indicating a specificity in cation interaction with the TOK1p gate. These and additional results indicate that external K+ acts as a ligand to inactivate the TOK1p channel, and they implicate a gating process mediated by a single cation binding site within the membrane electric field, but distinct from the permeation pathway.

Cloning and characterization of the first two genes of the non-oxidative part of the Saccharomyces cerevisiae pentose-phosphate pathway.

We have cloned and characterized the two remaining unknown genes of the non-oxidative part of the pentose-phosphate pathway of Saccharomyces cerevisiae encoding the enzymes D-ribulose-5-phosphate 3-epimerase (Rpe1p) and D-ribose-5-phosphate ketol-isomerase (Rki1p). Rpe1p has an unexpected high specific activity of 2148 mU x (mg protein)-1 in crude extracts. Deletion mutants of RPE1 show no enzyme activity and are unable to grow on D-xylulose. Unexpectedly, haploid rki1 deletion mutants are not viable. Functional expression of RKI1 was demonstrated following an increase of gene dosage in the haploid rki1 deletion mutant, which restored viability and specific D-ribose-5-phosphate ketol-isomerase activity. Both enzymes show high similarity to the deduced protein sequences of various open reading frames, expressed sequence tags or cDNAs from different organisms.

Sequence analysis of the CEN12 region of Saccharomyces cerevisiae on a 43.7 kb fragment of chromosome XII including an open reading frame homologous to the human cystic fibrosis transmembrane conductance regulator protein CFTR.

In the framework of the European Union BIOTECH project for systematically sequencing the Saccharomyces cerevisiae genome, we determined the nucleotide sequence of a 43.7 kb DNA fragment spanning the centromeric region of chromosome XII. A novel approach was the distribution of sublibraries prepared by the DNA coordinator (J. Hoheisel, Heidelberg, FRG), using a new hybridization-based DNA mapping method, in order to facilitate ordered sequencing. The sequence contains 22 open reading frames (ORFs) longer than 299 bp, including the published sequences for ATS/DPS1, SCD25, SOF1, DRS1, MMM1, DNM1 and the centromeric region CEN12. Five putative ORF products show similarity to known proteins: the leucine zipper-containing ABC transporter L1313p to the yeast Ycflp metal resistance protein, to the yeast putative ATP-dependent permease Yhd5p, to the yeast putative proteins Yk83p and Yk84p, to the human cystic fibrosis transmembrane conductance regulator protein (hCFTR) and to the human multidrug resistance-associated protein hMRP1; L1325p to the Drosophila melanogaster Pumilio protein, to the putative yeast regulatory protein Yg13p and to the yeast protein Mpt5p/Htrlp; L1329p to human lipase A and gastric lipase, to rat lingual lipase and to the putative yeast triglyceride lipase Tg11p; L1341p to the putative yeast protein Yhg4p; and the leucine zipper-containing L1361p to the two yeast proteins 00953p and Ym8156.08p and to the Arabidopsis thaliana protein HYP1. Eight ORFs show no homology to known sequences in the database, three small ORFs are internal and complementary to larger ones and L1301 is complementary overlapping the ATS/DPS1 gene. Additionally three equally spaced ARS consensus sequences were found.

A rapid and highly efficient method for PCR-based site-directed mutagenesis using only one new primer.

We present a rapid, cheap and highly efficient method for site-directed mutagenesis using the polymerase chain reaction (PCR). This method is applicable to every DNA fragment which has to be cloned into the multiple cloning site of any vector, or vector pair, in two different orientations. It requires only two primers, one new and specific mutagenic primer and one of the usual sequencing primers. In the first PCR, a mutagenic DNA fragment is synthesized which is amplified exponentially in the second PCR. In contrast, wild-type sequences are only linearly amplified resulting in an efficiency of mutagenesis of nearly 100%.

Sequence analysis of a 33.1 kb fragment from the left arm of Saccharomyces cerevisiae chromosome X, including putative proteins with leucine zippers, a fungal Zn(II)2-Cys6 binuclear cluster domain and a putative alpha 2-SCB-alpha 2 binding site.

In the framework of the European BIOTECH project for sequencing the Saccharomyces cerevisiae genome, we have determined the nucleotide sequence of the left part of the cosmid clone 232 and the cosmid clone 233 provided by F. Galibert (Rennes Cedex, France). We present here 33,099 base pairs of sequence derived from the left arm of chromosome X of strain S288C. This sequence reveals 17 open reading frames (ORFs) with more than 299 base pairs, including the published sequences for ARG3, LIGTR/LIG1, ORF2, ACT3 and SCP160. Two other ORFs showed similarity with S. cerevisiae genes: one with the CAN1 gene coding for an arginine permease, and one with genes encoding the family of transcriptional activators containing a fungal Zn(II)2-Cys6 binuclear cluster domain like that found in Ppr1p or Ga14p. Both putative proteins contain a leucine zipper motif, the Can1p homologue has 12 putative membrane-spanning domains and a putative alpha 2-SCB-alpha 2 binding site. In a diploid disruption mutant of ORF J0922 coding for the transcriptional activator homologue, no colonies appeared before 10 days after transformation and then grew slowly. In contrast, haploid disruption mutants showed a growth phenotype like wild-type cells. One ORF showed weak similarity to the rad4 gene product of Schizosaccharomyces pombe and is essential for yeast growth. Five ORFs showed similarity to putative genes on the right arm of chromosome XI of S. cerevisiae. Two of them have similarity to each other and belong to a family of extracellular proteins that groups mammalian SCP/Tpx-1, insects Ag3/Ag5, plants PR-1 and fungi Sc7/Sc14.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence and function analysis of a 9.74 kb fragment of Saccharomyces cerevisiae chromosome X including the BCK1 gene.

In the framework of the European BIOTECH project for sequencing the Saccharomyces cerevisiae genome, we have determined the nucleotide sequence of the cosmid clone 233 provided by F. Galibert (Rennes Cedex, France). We present here 9743 base pairs of sequence derived from the left arm of chromosome X. This sequence reveals three new open reading frames and includes the published sequence (5' end and open reading frame) of the gene BCK1/SLK1/SSP31 also identified as ORFAA. Deletion mutants of two earlier unknown open reading frames J0840 and J0904 are viable and the open reading frame J0902 is essential for yeast growth.

Sequence and function analysis of a 9.46 kb fragment of Saccharomyces cerevisiae chromosome X.

In the framework of the European yeast genome sequencing project, we have determined the nucleotide sequence of the cosmid clone 233 provided by F. Galibert (Rennes Cedex, France). We present here 9464 base pairs of this cosmid located on the left arm of Saccharomyces cerevisiae chromosome X. This sequence contains two new open reading frames and includes the published sequences of the RADH gene (also identified as SRS2/HPR5) and the 3'-end of the gene BCK1/SLK1/SSP31. Deletion mutants of the two unknown genes J0909 and J0911 are viable.

Lysine144 is essential for the catalytic activity of Saccharomyces cerevisiae transaldolase.

Replacement of lysine144 by glutamine in the pentose phosphate pathway enzyme transaldolase of Saccharomyces cerevisiae is associated with the complete loss of activity indicating the essential role in catalysis. Neither histidine nor cysteine is important for catalytic activity as proposed for the Candida utilis enzyme. Also we could not find any evidence for a half-site character of the enzyme as described for transaldolase of C. utilis. Therefore, the reaction mechanisms for the two enzymes are different.

Sequence and function analysis of a 2.73 kb fragment of Saccharomyces cerevisiae chromosome II.

The nucleotide sequence of a fragment of 2728 base pairs of Saccharomyces cerevisiae chromosome II has been determined. The sequence contains two open reading frames, one of them being incomplete. Deletion mutants of YBR11.21 are viable. YBR11.20 is identical to the recessive omnipotent suppressor SUP45 (SUP1).

Sequence of a 4.8 kb fragment of Saccharomyces cerevisiae chromosome II including three essential open reading frames.

The nucleotide sequence of a fragment of 4867 base pairs of Saccharomyces cerevisiae chromosome II has been determined. The sequence contains three complete open reading frames. In addition to the already known gene RPB5, coding for a subunit shared by all three DNA directed RNA polymerases, two new open reading frames could be identified. YBR12.03 codes for a protein of 183 amino acids with homology to one of the proteins of the Bacillus subtilis riboflavin biosynthesis operon (RibG). Deletion mutants of YBR12.03 can germinate but stop growing after five to seven cell divisions on YPD. Supplementation with high concentrations of riboflavin does promote growth. YBR12.05 codes for a protein of 386 amino acids with homology to STI1, a stress-inducible protein of S. cerevisiae. Deletion mutants of YBR12.05 are not viable.