XDJ1, a gene encoding a novel non-essential DnaJ homologue from Saccharomyces cerevisiae

The J- and G/F-domains of the major Synechocystis DnaJ protein Sll0897 are sufficient for cell viability but not for heat resistance

Hsp70 proteins and their Hsp40 co‐chaperones are essential components of cellular chaperone networks in both prokaryotes and eukaryotes. Here, we performed a genetic analysis to define the protein domains required for the key functions of the major Hsp40/DnaJ protein Sll0897 of the cyanobacterium Synechocystis sp. PCC6803. The expression of the N‐terminally located J‐ and G/F‐domains is essential and sufficient for the proteins’ fundamental in vivo functions, whereas the presence of the full‐length protein, containing the C‐terminal substrate‐binding domains, is crucial under stress conditions.

Recruitment of Cytosolic J-Proteins by TOM Receptors Promotes Mitochondrial Protein Biogenesis

Mitochondria possess elaborate machineries for the import of proteins from the cytosol. Cytosolic factors like Hsp70 chaperones and their co-chaperones, the J-proteins, guide proteins to the mitochondrial surface. The translocase of the mitochondrial outer membrane (TOM) forms the entry gate for preproteins. How the proteins are delivered to mitochondrial preprotein receptors is poorly understood. We identify the cytosolic J-protein Xdj1 as a specific interaction partner of the central receptor Tom22. Tom22 recruits Xdj1 to the mitochondrial surface to promote import of preproteins and assembly of the TOM complex. Additionally, we find that the receptor Tom70 binds a different cytosolic J-protein, Djp1. Our findings suggest that cytosolic J-proteins target distinct TOM receptors and promote the biogenesis of mitochondrial proteins.

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The receptor Tom22 recruits the cytosolic J-protein Xdj1 to mitochondria

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Xdj1 delivers preproteins to Tom22 and promotes biogenesis of the TOM complex

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The receptor Tom70 recruits a different cytosolic J-protein, Djp1

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Mitochondrial receptors selectively recognize cytosolic J-protein co-chaperones

Synthetic lethal interactions in yeast reveal functional roles of J protein co-chaperones

J proteins are a diverse family of co-chaperones that cooperate with heat shock protein 70 (Hsp70) to coordinate protein quality control, especially in response to cellular stress. Current models suggest that individual J proteins might play roles in recruiting Hsp70s to specific functions, such as maintaining cell wall integrity or promoting ribosome biogenesis. However, relatively few stresses have been used to test this model and, as a result, only a few specific activities have been identified. To expand our understanding of the J protein network, we used a synthetic lethal approach in which 11 Saccharomyces cerevisiae deletion strains were treated with 12 well-characterized chemical inhibitors. The results defined new roles for specific J proteins in major signaling pathways. For example, an important role for Swa2 in cell wall integrity was identified and activities of the under-explored Jjj1, Apj1, Jjj3 and Caj1 proteins were suggested. More generally, these findings support a model in which some J proteins, such as Ydj1 and Zuo1, play "generalist" roles, while others, such as Apj1 and Jjj2, are "specialists", having roles in relatively few pathways. Together, these results provide new insight into the network of J proteins.

An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell

Molecular chaperones are known to be involved in many cellular functions, however, a detailed and comprehensive overview of the interactions between chaperones and their cofactors and substrates is still absent. Systematic analysis of physical TAP-tag based protein–protein interactions of all known 63 chaperones in Saccharomyces cerevisiae has been carried out. These chaperones include seven small heat-shock proteins, three members of the AAA+ family, eight members of the CCT/TRiC complex, six members of the prefoldin/GimC complex, 22 Hsp40s, 1 Hsp60, 14 Hsp70s, and 2 Hsp90s. Our analysis provides a clear distinction between chaperones that are functionally promiscuous and chaperones that are functionally specific. We found that a given protein can interact with up to 25 different chaperones during its lifetime in the cell. The number of interacting chaperones was found to increase with the average number of hydrophobic stretches of length between one and five in a given protein. Importantly, cellular hot spots of chaperone interactions are elucidated. Our data suggest the presence of endogenous multicomponent chaperone modules in the cell.

The DnaJ family of protein chaperones in Trypanosoma cruzi

We have molecularly cloned four members of the DnaJ (heat shock protein 40) family of protein chaperones of the protozoan parasite Trypanosoma cruzi--tcj1, tcj2, tcj3 and tcj4. While all the proteins contain defining J domains at their N-termini, only tcj2, tcj3 and tcj4 contain glycine/phenylalanine-rich and zinc finger domains common to many other DnaJ homologues. Furthermore, tcj2 and tcj4 contain C-terminal CaaX motifs, substrates for prenyl modifications, suggesting that they are associated with cellular membranes. tcj1 is a divergent member of the family, containing neither glycine/phenylalanine-rich nor zinc finger domains. All the T. cruzi DnaJ genes are single copy, in contrast to other T. cruzi heat shock genes, which are arranged in multicopy direct tandem arrays. Among the tcj mRNAs, only tcj2 is heat inducible, which may result from posttranscriptional regulation involving a sequence found in the 3' untranslated regions of all heat-inducible T. cruzi mRNAs described to date. Further study of this important family of protein chaperones will aid our understanding of the protein folding and assembly processes in protozoans.

A conserved HPD sequence of the J-domain is necessary for YDJ1 stimulation of Hsp70 ATPase activity at a site distinct from substrate binding

The 46-kDa protein YDJ1 is one of several known yeast homologues of the Escherichia coli DnaJ protein. Like all J homologues, it shares homology with the highly conserved NH2-terminal "J-domain" of DnaJ. A component of the DnaK (Hsp70) chaperone machinery that mediates protein folding, DnaJ is necessary for survival at elevated temperatures. It stimulates ATP hydrolysis by DnaK and effects the release of DnaK-bound polypeptides. Previous genetic and biochemical studies indicate that the J-domain is necessary for these functions. Using peptides corresponding to J-domain sequence, we show that a peptide containing the highly conserved His-Pro-Asp sequence at positions 34-36 in the J-domain competes off YDJ1 stimulation of Hsp70 ATPase activity. Inhibitory concentrations of peptide do not prevent binding of folding substrates, therefore YDJ1 must interact with Hsp70 at a site distinct from that for substrate binding. This interaction is critical for Hsp70 activity, since a mutant YDJ1 protein harboring a H34Q change (ydj1Q34) stimulates neither Hsp70 ATPase nor substrate release. The importance of the proper function of this region of the protein is supported by the poor growth and temperature-sensitive phenotype of yeast expressing ydj1Q34.

Sequencing a cosmid clone of Saccharomyces cerevisiae chromosome XIV reveals 12 new open reading frames (ORFs) and an ancient duplication of six ORFs

A sequence of 31431 bp located on the left arm of chromosome (chr.) XIV from Saccharomyces cerevisiae was analysed. A total of 18 open reading frames (ORFs) could be identified. Twelve ORFs are new, two of which are most likely ribosomal protein genes, leaving ten ORFs of unknown function. Nine of the 18 ORFs show either at least 20% overall amino acid identity or significant regional homology to other S. cerevisiae ORFs. Additionally, six of these nine ORFs have homologues of similar size and the same transcriptional orientation within a stretch of 50 kb on chromosome IX. The degree of homology ranges from 90% overall identity to 23% in 375 amino acids. The homologues on chromosome IX are grouped in two blocks that are separated by relatively long ORFs. This is the first example of a multi-gene duplication in S. cerevisiae not linked to a centromere or subtelomere region.

Analysis of a 36.2 kb DNA sequence including the right telomere of chromosome VI from Saccharomyces cerevisiae

The nucleotide sequence of a 36.2-kb distal region containing the right telomere of chromosome VI was determined. Both strands of DNA cloned into cosmid clone 9965 and plasmid clone pEL174P2 were sequenced with an average redundancy of 7.9 per base pair, by both dye primer and dye terminator cycle sequencing methods. The G+C content of the sequence was found to be 37.9%. Eighteen open reading frames (ORFs) longer than 100 amino acids were detected. Four of these ORFs (9965orfR017, 9965orfF016, 9965orfR009 and 9965orfF003) were found to encode previously identified genes (YMR31, PRE4, NIN1 and HXK1, respectively). Six ORFs (9965orfR013, 9965orfF018, 9965orfF006, 9965orfR014, 9965orfF013 and 9965orfR020) were found to be homologous to hypothetical 121.4-kDa protein in the BCK 5' region, Bacillus subtilis DnaJ protein, hypothetical Trp-Asp repeats containing protein in DBP3-MRPL27, putative mitochondrial carrier YBR291C protein, Salmonella typhimurium nicotinate-nucleotide pyrophosphorylase, and Escherichia coli cystathionine beta-lyase, respectively. The putative proteins encoded by 9965orfF018, 9965orfR014 and 9965orfR020 were found to be, respectively, a new member of the family of DnaJ-like proteins, the mitochondrial carrier protein and cystathionine lyase.

Transcriptional regulation of the yeast DnaJ homologue SIS1

The Saccharomyces cerevisiae SIS1 gene encodes an essential heat shock protein with similarity to the Escherichia coli DnaJ protein. In sis 1-85 and sis1-86 mutants, the sis1 RNA is induced to high levels at room temperature and without heat shock. The presence of wild type SIS1 in the sis1-85 mutant represses the overexpression of SIS1-85 protein. Furthermore, overexpression of wild type SIS1 reduces the beta-galactosidase activity expressed from a SIS1:lacZ fusion. These results suggest that SIS1 negatively regulates its own expression. The autoregulation of SIS1 transcription is mediated through a 39-base pair cis-element containing the SIS1 heat shock element plus additional flanking sequences on one side. Although SIS1 transcription is constitutive, it is transiently induced upon heat shock. In addition, SIS1 transcription is regulated by SSA (a class of HSP70 proteins) function. The elevated transcription of SIS1 in ssa1 ssa2 mutants is mediated solely through the SIS1 heat shock element. Therefore, the SIS1 autoregulatory element is different from the SSA-responsive element, suggesting that the mechanism involved in autoregulation of SIS1 is distinct from regulation of SIS1 by SSA proteins.

Sequencing analysis of a 15.4 kb fragment of yeast chromosome XIV identifies the RPD3, PAS8 and KRE1 loci, five new open reading frames

The DNA sequence of a 15.4 kb region covering the left arm of chromosome XIV from Saccharomyces cerevisiae was determined. This region contains eight open reading frames (ORFs) which code for proteins of more than 100 amino acids. Three ORFs correspond to the RPD3, PAS8 and KRE1 loci, described previously. Three ORFs show limited homology with known proteins: NO330 with the recessive suppressor of secretory defect SAC1, NO325 with YCR094W identified during chromosome III sequencing; whereas NO315 presents a motif conserved in the dnaJ family. Two ORFs (NO320 and NO325) show no homology to known proteins within the databases screened, but NO320 corresponds to a serine-threonine-rich protein. The sequence has been entered in the EMBL data library under Accession Number Z46259.

Isolation of a mouse cDNA encoding MTJ1, a new murine member of the DnaJ family of proteins

We report the isolation and sequencing of MTJ1, a 1792-bp cDNA from an M27 murine lung carcinoma cell line. The largest ORF within MTJ1 encodes a 63,869-Da protein, containing a 73-amino-acid (aa) sequence (the J domain) that is conserved in proteins of the DnaJ family of chaperonins. The J domain of MTJ1 is bracketed by potential transmembrane domains in a similar configuration to the J domain of the yeast DnaJ-like protein, SEC63. Polyclonal antibodies raised against deduced aa sequences within MTJ1 recognized antigens of 62, 42 and 41 kDa that were enriched in the nuclear and heavy microsome subcellular fractions of murine tumor cells. Northern analysis detected a major 3.2-kb transcript that was present in all murine organs examined, but was relatively underexpressed in brain and heart.

Isolation and characterization of CAJ1, a novel yeast homolog of dnaJ

A novel member of the Escherichia coli dnaJ family, designated CAJ1, was isolated from a yeast expression library using antiserum against a yeast calmodulin-binding fraction. Although CAJ1 contains neither a Gly-rich region nor a Cys-rich repeat, as are found in other DnaJ relatives, it contains a leucine zipper-like motif.

Mdj1p, a novel chaperone of the DnaJ family, is involved in mitochondrial biogenesis and protein folding

Mdj1p, a novel member of the DnaJ family, is a heat shock protein that is associated with the inner membrane of mitochondria of Saccharomyces cerevisiae. Disruption of the MDJ1 gene resulted in a petite phenotype, loss of mitochondrial DNA, and inviability at 37 degrees C. Import of precursor proteins was not affected by a lack of Mdj1p, but folding of newly imported proteins was markedly impaired. The efficiency of refolding of a tester protein, dihydrofolate reductase, was significantly reduced in mitochondria lacking Mdj1p after incubation at elevated temperature. We conclude that Mdj1p is an important mitochondrial chaperone that participates in the folding of newly imported proteins and in the protection of proteins against heat denaturation and aggregation.