Cloning and genetic analysis of the gene encoding a new protein kinase in Saccharomyces cerevisiae

A NIMA-related kinase, Cnk2p, regulates both flagellar length and cell size in Chlamydomonas

The cycle of ciliogenesis and ciliary disassembly is coordinated with cell division. In the unicellular alga Chlamydomonas, the two flagella are maintained at constant and equal length during interphase, and are reabsorbed prior to mitosis. We report that the NIMA-related kinase, Cnk2p, is an axonemal protein that affects flagellar length via effects on disassembly rate and also plays a role in the cellular assessment of size prior to committing to mitosis. This is the second NIMA-related kinase shown to affect ciliary function and cell cycle progression in Chlamydomonas. We speculate that members of the NIMA family have evolved nuanced roles to coordinate cilia/cell cycle regulation.

A NIMA-related kinase, Fa2p, localizes to a novel site in the proximal cilia of Chlamydomonas and mouse kidney cells

Polycystic kidney disease and related syndromes involve dysregulation of cell proliferation in conjunction with ciliary defects. The relationship between cilia and cell cycle is enigmatic, but it may involve regulation by the NIMA-family of kinases (Neks). We previously showed that the Nek Fa2p is important for ciliary function and cell cycle in Chlamydomonas. We now show that Fa2p localizes to an important regulatory site at the proximal end of cilia in both Chlamydomonas and a mouse kidney cell line. Fa2p also is associated with the proximal end of centrioles. Its localization is dynamic during the cell cycle, following a similar pattern in both cell types. The cell cycle function of Fa2p is kinase independent, whereas its ciliary function is kinase dependent. Mice with mutations in Nek1 or Nek8 have cystic kidneys; therefore, our discovery that a member of this phylogenetic group of Nek proteins is localized to the same sites in Chlamydomonas and kidney epithelial cells suggests that Neks play conserved roles in the coordination of cilia and cell cycle progression.

The protein kinases of budding yeast: six score and more

The completion of the budding yeast genome sequencing project has made it possible to determine not only the total number of genes, but also the exact number of genes of a particular type 1-3. As a consequence, we now know exactly how many protein kinases are encoded by the yeast genome, a number of considerable interest because of the importance of protein phosphorylation in the control of so many cellular processes.

Sequence and analysis of a 26.9 kb fragment from chromosome XV of the yeast Saccharomyces cerevisiae

We have determined the nucleotide sequence of a fragment of chromosome XV of Saccharomyces cerevisiae cloned into cosmid pEOA048. The analysis of the 26,857 bp sequence reveals the presence of 19 open reading frames (ORFs), and of one RNA-coding gene (SNR17A). Six ORFs correspond to previously known genes (MKK1/SSP32, YGE1/GRPE/MGE1, KIN4/KIN31/KIN3, RPL37B, DFR1 and HES1, respectively), all others were discovered in this work. Only five of the new ORFs have significant homologs in public databases, the remaining eight correspond to orphans (two of them are questionable). O5248 is a probable folypolyglutamate synthetase, having two structural homologs already sequenced in the yeast genome. O5273 shows homology with a yeast protein required for vanadate resistance. O5268 shows homology with putative oxidoreductases of different organisms. O5257 shows homology with the SAS2 protein and another hypothetical protein from yeast. The last one, O5245, shows homology with a putative protein of Caenorhabditis elegans of unknown function. The present sequence corresponds to coordinates 772,331 to 799,187 of the entire chromosome XV sequence which can be retrieved by anonymous ftp (ftp. mips. embnet. org).

Mitochondrial GrpE is present in a complex with hsp70 and preproteins in transit across membranes

We characterized a 24-kDa protein associated with matrix hsp70 (mt-hsp70) of Neurospora crassa and Saccharomyces cerevisiae mitochondria. By using specific antibodies, the protein was identified as MGE, a mitochondrial homolog of the prokaryotic heat shock protein GrpE. MGE extracted from mitochondria was quantitatively bound to hsp70. It was efficiently released from hsp70 by the addition of Mg-ATP but not by nonhydrolyzable ATP analogs or high salt. A mutant mt-hsp70, which was impaired in release of bound precursor proteins, released MGE in an ATP-dependent manner, indicating that precursor proteins and MGE bind to different sites of hsp70. A preprotein accumulated in transit across the mitochondrial membranes was specifically coprecipitated by either antibodies directed against MGE or antibodies directed against mt-hsp70. The preprotein accumulated at the outer membrane was not coprecipitated by either antibody preparation. After being imported into the matrix, the preprotein could be coprecipitated only by antibodies against mt-hsp70. We propose that mt-hsp70 and MGE cooperate in membrane translocation of preproteins.

Mitochondrial GrpE is present in a complex with hsp70 and preproteins in transit across membranes

We characterized a 24-kDa protein associated with matrix hsp70 (mt-hsp70) of Neurospora crassa and Saccharomyces cerevisiae mitochondria. By using specific antibodies, the protein was identified as MGE, a mitochondrial homolog of the prokaryotic heat shock protein GrpE. MGE extracted from mitochondria was quantitatively bound to hsp70. It was efficiently released from hsp70 by the addition of Mg-ATP but not by nonhydrolyzable ATP analogs or high salt. A mutant mt-hsp70, which was impaired in release of bound precursor proteins, released MGE in an ATP-dependent manner, indicating that precursor proteins and MGE bind to different sites of hsp70. A preprotein accumulated in transit across the mitochondrial membranes was specifically coprecipitated by either antibodies directed against MGE or antibodies directed against mt-hsp70. The preprotein accumulated at the outer membrane was not coprecipitated by either antibody preparation. After being imported into the matrix, the preprotein could be coprecipitated only by antibodies against mt-hsp70. We propose that mt-hsp70 and MGE cooperate in membrane translocation of preproteins.

A role for a eukaryotic GrpE-related protein, Mge1p, in protein translocation

The 70-kDa heat shock proteins (hsp70s) function as molecular chaperones in a wide variety of cellular processes through cycles of binding and release from substrate proteins coupled to cycles of ATP hydrolysis. In the prokaryote Escherichia coli, the hsp70 DnaK functions with two other proteins, DnaJ and GrpE, which modulate the activity of DnaK. While numerous hsp70s and DnaJ-related proteins have been identified in eukaryotes, to our knowledge no GrpE-related proteins have been reported. We report the isolation and characterization of a eukaryotic grpE-related gene, MGE1. MGE1, an essential nuclear gene of the yeast Saccharomyces cerevisiae, encodes a soluble protein of the mitochondrial matrix. Cells with reduced expression of Mge1p accumulate the precursor form of a mitochondrial protein. Since mitochondrial hsp70 is required for translocation of precursors of mitochondrial proteins from the cytosol into the matrix of mitochondria, these data suggest that Mge1p acts in concert with mitochondrial hsp70 in protein translocation.

Saccharomyces cerevisiae ribosomal protein L37 is encoded by duplicate genes that are differentially expressed

A duplicate copy of the RPL37A gene (encoding ribosomal protein L37) was cloned and sequenced. The coding region of RPL37B is very similar to that of RPL37A, with only one conservative amino-acid difference. However, the intron and flanking sequences of the two genes are extremely dissimilar. Disruption experiments indicate that the two loci are not functionally equivalent: disruption of RPL37B was insignificant, but disruption of RPL37A severely impaired the growth rate of the cell. When both RPL37 loci are disrupted, the cell is unable to grow at all, indicating that rpL37 is an essential protein. The functional disparity between the two RPL37 loci could be explained by differential gene expression. The results of two experiments support this idea: gene fusion of RPL37A to a reporter gene resulted in six-fold higher mRNA levels than was generated by the same reporter gene fused to RPL37B, and a modest increase in gene dosage of RPL37B overcame the lack of a functional RPL37A gene.

YGE1 is a yeast homologue of Escherichia coli grpE and is required for maintenance of mitochondrial functions

The grpE gene is a heat shock gene of Escherichia coli whose product functions as a chaperone to (re)fold proteins. We found a yeast homologue of grpE and designated it YGE1. YGE1 can replace grpE in E. coli, indicating that YGE1 is a functional homologue of grpE. Deletion of YGE1 is lethal. During depletion of the Yge1 product, mitochondria are sequestered in mother cells thereby accumulating cells without mitochondria, suggesting that Yge1 protein plays a pivotal role in maintaining mitochondrial functions.