The c-Cbl protein is tyrosine phosphorylated and forms complexes with a wide range of signalling partners in response to various growth factors. How c-Cbl interacts with proteins, such as Grb2, phosphatidylinositol 3-kinase, and phosphorylated receptors, is well understood, but its role in these complexes is unclear. Recently, the Caenorhabditis elegans Cbl homolog, Sli

We identified a new, unique upstream activating sequence (5P P-GGTGGCAAA-3P P) in the promoters of 26 out of the 32 proteasomal yeast genes characterized to date, which we propose to call proteasome-associated control element. By using the one-hybrid method, we show that the factor binding to the proteasome-associated control element is Rpn4p, a protein containing a C2H2-type finger motif and two acidic domains. Electrophoretic mobility shift assays using proteasome-associated control element sequences from two regulatory proteasomal genes confirmed specific binding of purified Rpn4p to these sequences. The role of Rpn4p to function as a transregulator in yeast is corroborated by its ability of stimulating proteasomeassociated control element-driven lacZ expression and by experiments using the RPT4 and RPT6 gene promoters coupled to the bacterial cat gene as a reporter. Additionally, we found the proteasome-associated control element to occur in a number of promoters to genes which are related to the ubiquitin-proteasome pathway in yeast.z 1999 Federation of European Biochemical Societies.

There is accumulating evidence for a large, highly conserved gene family of putative ATPases. We have identified 12 different members of this novel gene family (the YTA family) in yeast and determined the nucleotide sequences of nine of these genes. All of the putative gene products are characterized by the presence of a highly conserved domain of 300 amino acids containing specialized forms of the A and B boxes of ATPases. YTA1, YTA2, YTA3 and YTA5 exhibit significant similarity to proteins involved in human immunodeficiency virus Tat-mediated gene expression but more significantly to subunits of the human 26S proteasome. YTA1 and YTA2 are essential genes in yeast. Remarkably, the cDNA of human TBP-1 can compensate for the loss of YTA1. Preliminary experiments indicate that YTA1 is a component of the 26S protease complex from yeast. Our findings lead us to propose that YTA1, YTA2, YTA3 and YTA5 function as regulatory subunits of the yeast 26S proteasome. YTA10, YTA11 and YTA12 share significant homology with the Escherichia coli FtsH protein, and together with YTA4 and YTA6 may constitute a separate subclass within this family of putative ATPases.

Siah proteins function as E3 ubiquitin ligase enzymes to target the degradation of diverse protein substrates. To characterize the physiological roles of Siah2, we have generated and analyzed Siah2 mutant mice. In contrast to Siah1a knockout mice, which are growth retarded and exhibit defects in spermatogenesis, Siah2 mutant mice are fertile and largely phenotypically normal. While previous studies implicate Siah2 in the regulation of TRAF2, Vav1, OBF-1, and DCC, we find that a variety of responses mediated by these proteins are unaffected by loss of Siah2. However, we have identified an expansion of myeloid progenitor cells in the bone marrow of Siah2 mutant mice. Consistent with this, we show that Siah2 mutant bone marrow produces more osteoclasts in vitro than wild-type bone marrow. The observation that combined Siah2 and Siah1a mutation causes embryonic and neonatal lethality demonstrates that the highly homologous Siah proteins have partially overlapping functions in vivo.

Akstraet The yeast gene, YTAIO, encodes a member of a novel family of putative ATPases. Ytal0p, as deduced from the nucleotide sequence, is 761 amino acids in length (predicted molecular mass 84.5 kDa). The amino acid sequence of Yta 10p exhibits high similarity to two other yeast proteins, Ytal 1 and Ytal2, and to E. coli FtsH. Several features of Ytal0p are compatible with its localization in mitochondria. We report here that Ytal0p is a yeast mitochondrial protein and that import is dependent on a membrane potential and accompanied by processing to a protein of approximately 73 kDa. Disruption of YTAIO leads to a nuclear petite phenotype and to a loss of respiratory competence, as shown by spectrophotometric measurement of the activities of respiratory complexes I-III and IV, respectively. These findings together with the high similarity of Ytal0p to several ATP-dependent proteases suggest that Ytal0p is a mitochondrial component involved, directly or indirectly, in the correct assembly and/or maintenance of active respiratory complexes.