Interactions of phosphatidylinositol kinase, GTPase-activating protein (GAP), and GAP-associated proteins with the colony-stimulating factor 1 receptor

The interactions of the macrophage colony-stimulating factor 1 (CSF-1) receptor with potential targets were investigated after ligand stimulation either of mouse macrophages or of fibroblasts that ectopically express mouse CSF-1 receptors. In Rat-2 cells expressing the mouse CSF-1 receptor, full activation of the receptor and cellular transformation require exogenous CSF-1, whereas NIH 3T3 cells expressing mouse c-fms are transformed by autocrine stimulation. Activated CSF-1 receptors physically associate with a phosphatidylinositol (PI) 3'-kinase. A mutant CSF-1 receptor with a deletion of the kinase insert region was deficient in its ability to bind functional PI 3'-kinase and to induce PI 3'-kinase activity precipitable with antiphosphotyrosine antibodies. In fibroblasts, CSF-1 stimulation also induced the phosphorylation of the GTPase-activating protein (GAP)-associated protein p62 on tyrosine, although GAP itself was a relatively poor substrate. In contrast to PI 3'-kinase association, phosphorylation of p62 and GAP was not markedly affected by deletion of the kinase insert region. These results indicate that the kinase insert region selectively enhances the CSF-1-dependent association of the CSF-1 receptor with active PI 3'-kinase. The insert deletion mutant retains considerable transforming activity in NIH 3T3 cells (G. Taylor, M. Reedijk, V. Rothwell, L. Rohrschneider, and T. Pawson, EMBO J. 8:2029-2037, 1989). This mutant was more seriously impaired in Rat-2 cell transformation, although mutant-expressing Rat-2 cells still formed small colonies in soft agar in the presence of CSF-1. Therefore, phosphorylation of GAP and p62 through activation of the CSF-1 receptor does not result in full fibroblast transformation. The interaction between the CSF-1 receptor and PI 3'-kinase may contribute to c-fms fibroblast transformation and play a role in CSF-1-stimulated macrophages.

An amino-terminal signal sequence abrogates the intrinsic membrane-targeting information of mitochondrial uncoupling protein

Mitochondrial uncoupling protein, a polytopic integral protein of the inner membrane, is initially made in the cytoplasm as a soluble polypeptide (307 amino acids) lacking a cleavable targeting (signal) peptide. Earlier studies (Liu, X., Bell, A. W., Freeman, K. B., and Shore, G. C. (1988) J. Cell Biol. 107, 503-509) identified internal regions of the molecule that are critical for targeting and membrane insertion. Here, we demonstrate that the ability of uncoupling protein to insert into the inner membrane is abrogated when the molecule is fused behind the matrix-targeting signal of preornithine carbamyltransferase; the hybrid protein was imported across the inner membrane and deposited in the matrix where it was processed. In this context, however, the processed product remained in the matrix and was incapable of inserting into the inner membrane.

[A study on the promotion of adhesion properties of adhesives to metals treated by positive oxidation]

The adhesion to three alloys: Durabond, GH30 and soft Co-Cr, by PE adhesive was investigated. The surfaces of metals were treated by polishing, sand-blasting, positive-oxidation and complex processing in order to test the tensile bond strengths between metals and PE adhesive; to study the effects of the surface treatment of metals on adhesive properties; and to compare the tensile strength with that from the control experiment with EB composite resin and Panavia-EX resin under the same conditions. The results showed the mean tensile bond strengths between PE adhesive and Durabond, GH30 and soft Co-Cr alloys after the treatment of sandblasting and positive oxidation were 214.65 +/- 51.68 kg/cm2, 372.88 +/- 21.88 kg/cm2 and 349.21 +/- 48.32 kg/cm2 respectively, displaying better adhesive properties and stability of resistance to water.

Chloroplast ribosomal protein gene rps12 of Chlamydomonas reinhardtii. Wild-type sequence, mutation to streptomycin resistance and dependence, and function in Escherichia coli

The chloroplast rps12 gene encoding ribosomal protein S12 from wild-type as well as from streptomycin-resistant and -dependent mutants of Chlamydomonas reinhardtii was cloned and sequenced. At least six mRNA transcripts ranging in size from 800 to 4800 nucleotides were found to contain the rps12 coding sequence. As in Escherichia coli and Euglena, the C. reinhardtii rps12 gene is continuous, in contrast to its trans-spliced structure in higher plants. However, rps12 of C. reinhardtii is no longer immediately adjacent to the rps7 gene encoding ribosomal protein S7 as it is in other organisms. The deduced amino acid sequence of C. reinhardtii S12 protein shows strong homologies (48-79% identity) to S12 protein sequences of other organisms, but it has extra amino acid residues at its C terminus. Single base pair changes at different sites result in streptomycin-resistant or -dependent mutants with amino acid changes identical to comparable mutations in the E. coli S12 protein. The chloroplast rps12 gene is also expressed under the control of its own promoter in E. coli cells, and the C. reinhardtii S12 protein produced assembles into the E. coli ribosomes where it appears to function efficiently.

[Observation on enhanced adhesion to dentin by amino acid]

An amino acid was adopted to pretreat the surface of dentin. The bond strength between GP adhesive and dentin mediated by the amino acid was enhanced after the pretreatment. Furthermore, the longer the stored time of extracted tooth was, the better the effect of adhesion was. This pretreatment will benefit the adhesive restoration for dead tooth or low activity tooth clinically.

[Effects of test conditions on tensile bond strength to dentin]

The purpose of the paper was to investigate the effects of four test conditions on tensile bond strength to dentin, which included: (1) the area of tooth bonded, (2) tensile speed, (3) the fresh degree of tooth, (4) the times of tooth used. For GP dentin bonding agent, the results indicated: 1. There was no obvious effect of the bonded area on the bond strength. Both occlusal face and buccal face could be adopted. 2. There was no evident effect of the tensile speed on the bond strength. Any tensile speed could be chosen within some extent. 3. The bond strength greatly depended on the fresh degree of tooth. The longer the period of tooth stored after extraction was, the lower the bond strength was. Tooth used should be within 1 month after extraction. 4. There was obvious relationship between the bond strength and the times of tooth used. The more the tooth was repeatedly used, the lower the bond strength was. Tooth might only be used once.

mRNAs for two ribosomal proteins are preferentially translated in the chloroplast of Chlamydomonas reinhardtii under conditions of reduced protein synthesis

Two mutants of the green alga Chlamydomonas reinhardtii, one deficient in the small subunit of the chloroplast ribosome and the other having chloroplast ribosomes with reduced function under certain conditions, show a characteristic syndrome of photosynthetic defects resulting from reduced chloroplast protein synthesis. These include subnormal levels of ribulose 1,5-bisphosphate carboxylase (Rubisco), reduced Hill reaction activity, diminished capacity to fix CO2, and abnormal thylakoid stacking. However, these mutants accumulate normal appearing chloroplast ribosome monomers or large subunits containing normal ribosomal protein components. In this paper, we demonstrate that pulse-labeled cells of these mutants synthesize two large subunit chloroplast ribosomal proteins at about 60% of the wild-type rate, whereas Rubisco large subunit (LSU) and the alpha subunit of CF1 are made at only 4 to 8% of the wild-type rate. No difference in the rate of turnover between ribosomal proteins and Rubisco LSU in mutant and wild-type cells was observed during a subsequent 60 min chase. Differences between the mutants and wild-type cells in the relative synthesis rates of these proteins were not reflected in the relative levels of mRNA (either hybridizable or in vitro translatable). In aggregate, these data suggest that C. reinhardtii preferentially translates chloroplast ribosomal protein mRNAs under conditions of reduced total chloroplast protein synthesis.

Chloroplast ribosomal protein L-18 in Chlamydomonas reinhardtii is processed during ribosome assembly

Chloroplast ribosomal protein L-18 is made in the cytoplasm as a precursor, imported into the chloroplast, and processed to the mature form in two steps. We report here that the intermediate produced following the first processing step associates specifically with a ribosomal complex migrating with the chloroplast ribosome large subunit peak in sucrose gradients, and is then processed into mature L-18. This processing event is slowed down in mutant cells deficient in synthesis of non-ribosomal proteins in the chloroplast. Thus the second processing step of L-18 occurs during ribosome assembly, depends on one or more nonribosomal proteins made in the chloroplast, and may be required for the maturation of the 50 S ribosome subunit. The mature L-18 protein shows extensive sequence homology at its amino-terminus to Escherichia coli ribosomal protein L27, which is located at the interface between 30 S and 50 S subunits and is involved in the formation of the peptidyl-tRNA binding site.

Topogenesis of mitochondrial inner membrane uncoupling protein. Rerouting transmembrane segments to the soluble matrix compartment

Brown adipose tissue uncoupling protein (UCP), an integral polytopic protein of the mitochondrial inner membrane, is composed of at least six transmembrane segments whose net hydrophobic character derives from paired amphiphilic helices. The protein is synthesized in the cytoplasm as a polypeptide (307 amino acids) lacking a cleavable targeting (signal) peptide. Deletion mutagenesis and fusion protein constructions revealed the existence of at least two import signals: one lying between UCP precursor amino acids 13-105 and the other downstream of position 101. The former resulted in both targeting and membrane insertion of a fusion protein, whereas the latter targeted UCP 102-307 into the organelle but failed to result in membrane insertion. When a strong matrix-targeting signal derived from precarbamoyl phosphate synthetase was fused to UCP amino acids 169-307 or 52-307 (containing three and five transmembrane domains, respectively), the fusion proteins were efficiently imported to the soluble matrix compartment where correct signal cleavage took place. We suggest that assembly of UCP into the inner membrane follows a coordinate insertion pathway for integration and may use more than one signal sequence to achieve this. In this respect, it might share certain mechanistic features with the insertion of polytopic proteins into the endoplasmic reticulum. The data also suggest, however, that integration of the amino-terminal third of UCP into the inner membrane may be required to help or enhance insertion of the remaining UCP transmembrane domains.

Effects of lipid peroxides on prostacyclin and thromboxane generation in hypercholesterolemic rabbits

Rabbits fed an atherogenic diet for 60 days resulted in high levels of plasma lipid peroxides as well as extreme hypercholesterolemia. Both levels stayed high until 35 days after the atherogenic diet stopped. At the same time, plasma PGI2 level was remarkably decreased while TXA2 and platelet aggregability were increased. Atherosclerotic aortas contain high levels of lipid peroxides associated with decreased PGI2 and increased TXA2 generation. Atherosclerotic plaques had the highest level of lipid peroxides and TXA2 while PGI2 production was the least, as compared with nonplaque tissue of the same artery and the normal arteries. The condition of normal arteries was just the reverse. There was a negative correlation between lipid peroxides and prostacyclin production, and a positive correlation between lipid peroxides and TXA2, in both plasma and aorta of rabbits. These results suggest that there is a close correlation between atherosclerosis, elevated lipid peroxides, and disturbances in PGI2/TXA2 balances.

Triazine monomers and their adhesion to dentin

A series of 4,6-dichloro-1,3,5-triazines [e.g., 2-allylamino-(ADT), diallylamino-(DADT), 2-N-p-allyloxyphenylamino-, 2-N-allyl-N-phenylamino-, and 2-N-allyl-N-p-tolylamino-4,6-dichloro-1,3,5-triazine] was synthesized and characterized by IR, NMR, and mass spectrometry. These monomers have chlorine atoms that can react with NH2 or OH groups and double bonds capable of copolymerization. Aniline reacted readily with ADT and DADT, ethanol reacted with ADT, but acetone, H2O, and DMF did not react with either triazine. It appears that ADT or DADT will react with dentinal collagen through NH2 or OH groups in the peptide side-chains. An aprotic solvent should be used for ADT or DADT, but absolute dryness in clinical usage is not essential because of the slow hydrolysis of ADT and DADT. Stability of the N-di-substituted amino derivative (DADT) is greater than that of the mono-substituted compound (ADT), which may isomerize. ADT and methyl methacrylate were copolymerized at 37 degrees C with amine-peroxide. ADT solutions enhanced the adhesive strength of restorative resin to dentin. Thus, monomers such as ADT and DADT appear to be promising dentin-bonding agents.

Neutral peptidases in the stroma of pea chloroplasts

One endopeptidase (EP1) and at least three aminopeptidases (AP1, AP2, and AP3) were discovered in the stroma of chloroplasts isolated from pea seedlings (Pisum sativum L.), and purified over 100-fold. EP1 requires added Mg(2+) or Ca(2+) for activity, may have an additional tightly bound metal atom, and is inhibited by sulfhydryl reagents but not by serine residue-directed inhibitors. It is reversibly inhibited by dithiothreitol. Its specificity is for the bond between two adjacent Ala or Gly residues. Its molecular mass is 93 kilodaltons, estimated on a gel filtration column. Aminopeptidase activities were detected with the aid of different amino acyl-beta-naphthylamides as substrates. They were resolved into at least three individual proteins by gel filtration and DEAE-cellulose chromatography, having apparent molecular masses of 269,000 (AP1), 84,000 (AP2), and 42,000 (AP3) daltons, respectively. Each has a unique specificity for substrates, with AP1 hydrolyzing only the Prolyl-beta-naphthylamide. None of the APs require added divalent cations for activity, but the possibility of a tightly bound metal function was suggested in AP2 and AP3 (not AP1) from effects of inhibitors. A probable sulfhydryl residue function was indicated for all three, from inhibition by p-hydroxymercuribenzoate and Zn(2+). All these peptidases had pH optima at 7.7.