Disassembly and gross structure of particulate aminoacyl-tRNA synthetases from rat liver. Isolation and the structural relationship of synthetase complexes.

The major high molecular weight complex of aminoacyl-tRNA synthetases is purified about 1000-fold with 30% yield from rat liver. The synthetase complex sediments at 24 S with a molecular weight of 900,000 +/- 75,000 and contains aminoacylation activities for lysine, arginine, isoleucine, leucine, methionine, glutamine, glutamate, and proline. The 24 S synthetase complex dissociates into 21 S, 18 S, 13 S, 12 S, and 10 S complexes with specific enzymatic activities. Dissociation of the 24 S complex into active free synthetases is achieved by hydrophobic interaction chromatography. The disassembly of the synthetase complex is consistent with the structural model of a heterotypic multienzyme complex and suggests that the complex formation is due to the specific intermolecular interactions among the synthetases.

Purification and characterization of lysyl-tRNA synthetase after dissociation of the particulate aminoacyl-tRNA synthetases from rat liver.

The major aminoacyl-tRNA synthetase complex (the 24 S complex) isolated from rat liver, which contains lysyl-, leucyl-, and arginyl-tRNA synthetase activities, is dissociated into fully active free aminoacyl-tRNA synthetases by column chromatography on diaminooctyl-Sepharose. During the hydrophobic interaction chromatography, more than a quantitative yield of the lysyl-tRNA synthetase activity is obtained. The free lysyl-tRNA synthetase, dissociated from the synthetase complex, is purified about 2,000-fold with a 13% yield by conventional column chromatography. Lysyl-tRNA synthetase is also purified from the 24 S synthetase complex by affinity column chromatography on lysyl-diaminohexyl-Sepharose. Free lysyl-tRNA synthetase as dissociated from the synthetase complex, is evidently a dimeric enzyme with a subunit molecular weight of 66,000 +/- 3,000, as determined by gel electrophoresis, sucrose gradient centrifugation and gel filtration.

A humoral factor in the plasma of dogs with hemorrhagic hypotension causing histopathologic changes when infused into normals.

The presence of circulating factors in the plasma of shocked dogs which would be capable of causing lung lesions when infused into normotensive dogs was demonstrated by light and electron microscopy. Light microscopy only identified significant differences in atelectasis, vascular congestion, and interstitial edema in the shock and shock-plasma recipient animals. On electron microscopy, interstitial edema and disruption of collagen bundles were consistently found in shocked dogs and in dogs that had received shocked plasma. There was a consistent increase in pulmonary interstitial sodium in both shock and shock-plasma recipient groups. It is concluded that a plasma factor present in the serum of shocked dogs may be transferred to other dogs and cause histopathologic changes seen in the lungs of shocked animals.

Physical and biochemical characterization of a purified arginyl-tRNA synthetase-lysyl-tRNA-synthetase complex from rat liver.

Arginyl- and lysyl-tRNA synthetases copurify throughout a six-step chromatographic procedure resulting in a purification of 605- and 559-fold, respectively. The purified enzymes were estimated to be 98% pure with a stoichiometry of 1:1 from acrylamide gel electrophoresis under denaturing conditions. On the basis of a native molecular weight of 285000 calculated from s20,w, Rs, and V and subunit molecular weights of 73000 and 65000 obtained by sodium dodecyl sulfate gel electrophoresis, the synthetases appear to exist as a tetramer. The tetrameric structure was also supported by cross-linking studies. These results are consistent with an alpha 2 beta 2 structure, but an alpha beta structure has not been ruled out.

Overexpression of cyclin D1 in the Dami megakaryocytic cell line causes growth arrest.

The maturation of megakaryocytes in vivo requires polyploidization or repeated duplication of DNA without cytokinesis. As DNA replication and cytokinesis are tightly regulated in somatic cells by cyclins and cyclin-dependent kinases, we sought to determine the pattern of cyclin gene expression in cells that undergo megakaryocytic differentiation and polyploidization. The Dami megakaryocytic cell line differentiates and increases ploidy in response to phorbol 12-myristate 13-acetate (PMA) stimulation in vitro. We used Northern blotting to analyze mRNA levels of cyclins A, B, C, D1, and E in PMA-induced Dami cells and found that cyclin D1 mRNA levels increased dramatically (18-fold). Similar increases in cyclin D1 mRNA were obtained for other cell lines (HEL and K562) with megakaryocytic properties, but not in HeLa cells. The increase in cyclin D1 was confirmed by Western immunoblotting of PMA-treated Dami cells. This finding suggested that cyclin D1 might participate in megakaryocyte differentiation by promoting endomitosis and/or inhibiting cell division. To address these possibilities, we constructed two stable Zn+2-inducible, cyclin D1-overexpressing Dami cell lines. Cyclin D1 expression alone was not sufficient to induce polyploidy, but in conjunction with PMA-induced differentiation, polyploidization was slightly enhanced. However, unlike other cell systems, cyclin D1 overexpression caused cessation of cell growth. Although the mechanism by which cyclin D1 may affect megakaryocyte differentiation is not clear, these data demonstrate that cyclin D1 is upregulated in differentiating megakaryocytic cells and may contribute to differentiation by arresting cell proliferation.

Karyoplasmic interaction selection strategy: a general strategy to detect protein-protein interactions in mammalian cells.

We describe a strategy and reagents for study of protein-protein interactions in mammalian cells, termed the karyoplasmic interaction selection strategy (KISS). With this strategy, specific protein-protein interactions are identified by reconstitution of the functional activity of the yeast transcriptional activator GAL4 and the resultant transcription of a GAL4-regulated reporter gene. Reconstitution of GAL4 function results from specific interaction between two chimeric proteins: one contains the DNA-binding domain of GAL4; the other contains a transcriptional activation domain. Transcription of the reporter gene occurs if the two chimeric proteins can form a complex that reconstitutes the DNA-binding and transcriptional activation functions of GAL4. Using the KISS system, we demonstrate specific interactions for sequences from three different pairs of proteins that complex in the cytoplasm. In addition, we demonstrate that reporter genes encoding cell surface or drug-resistance markers can be specifically activated as a result of protein-protein interactions. With these selectable markers, the KISS system can be used to screen specialized cDNA libraries to identify novel protein interactions.