SEARCH · Search PubMed

Results for “Assembly process”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources

PubMed1984

Subcellular distribution of ribosomal proteins S6 and eL12. Analysis by autoradiography and immunofluorescence of sections from oocytes of Xenopus laevis.

The process of ribosome assembly in eukaryotes was studied by injecting tritium-labeled ribosomal proteins S6 and eL12 into oocytes of Xenopus laevis. The subcellular distribution of the two proteins was visualized by means of autoradiography in sections of oocytes. Protein S6 but not eL12 was found in the nucleus where it accumulated at the nucleoli. In the presence of actinomycin D the accumulation of S6 at the nucleoli was reduced. In-situ immunofluorescence studies indicated that S6 is located at the nucleoli and eL12 exclusively in the cytoplasm. It appears that S6 is involved in the early ribosomal assembly process at the nucleoli, whereas eL12 is restricted to the cytoplasm where it is incorporated into 60S ribosomal subunits in a late assembly step.

Animals↗

PubMed1987

Site-specific mutations at a picornavirus VP3/VP1 cleavage site disrupt in vitro processing and assembly of capsid precursors.

Most proteolytic cleavages within the picornavirus polyproteins are carried out by viral protease 3C. For encephalomyocarditis virus, the protease 3C-catalyzed processing occurs between Gln-Gly or Gln-Ser amino acid pairs which are flanked by proline residues, but the sequence-specific constraints on recognition and cleavage by the enzyme are not completely understood. To examine alternative cleavage site sequences, we constructed a cDNA plasmid which expresses the viral L-P1-2A capsid precursor in vitro and introduced site-specific mutations into the Gln-Gly pair at the VP3/VP1 junction. The altered protein substrates were tested for cleavage activity in assays with protease 3C. The encephalomyocarditis virus 3C processed Gln-Ala as efficiently as its natural sites but did not cleave Gln-Val, Gln-Glu, Lys-Gly, Lys-Ala, Lys-Val, Lys-Glu, or Pro-Gly combinations. Displacement of the flanking proline residue by an engineered insertion slowed but did not prevent cleavage at this site. Also, a mutant defective in processing at the VP3/VP1 junction was unable to form 14S pentameric assembly intermediates in vitro.

Base Sequence↗

PubMed1991

The hepatitis A virus polyprotein expressed by a recombinant vaccinia virus undergoes proteolytic processing and assembly into viruslike particles.

Hepatitis A virus (HAV) contains a single-stranded, plus-sense RNA genome with a single long open reading frame encoding a polyprotein of approximately 250 kDa. Viral structural proteins are generated by posttranslational proteolytic processing of this polyprotein. We constructed recombinant vaccinia viruses which expressed the HAV polyprotein (rV-ORF) and the P1 structural region (rV-P1). rV-ORF-infected cell lysates demonstrated that the polyprotein was cleaved into immunoreactive 29- and 33-kDa proteins which comigrated with HAV capsid proteins VP0 and VP1. The rV-P1 construct produced a 90-kDa protein which showed no evidence of posttranslational processing. Solid-phase radioimmunoassays with human polyclonal anti-HAV sera and with murine or human neutralizing monoclonal anti-HAV antibodies recognized the rV-ORF-infected cell lysates. Sucrose density gradients of rV-ORF-infected cell lysates contained peaks of HAV antigen with sedimentation coefficients of approximately 70S and 15S, similar to those of HAV empty capsids and pentamers. Immune electron microscopy also demonstrated the presence of viruslike particles in rV-ORF-infected cell lysates. Thus, the HAV polyprotein expressed by a recombinant vaccinia virus demonstrated posttranslational processing into mature capsid proteins which assembled into antigenic viruslike particles.

Base Sequence↗

PubMed1990

Switching in the self-assembly of tobacco mosaic virus.

Experimental observations on the structure and physicochemical properties of TMV protein assemblies have led to a fundamental switch in the model of the self-assembly process: rather than being nucleated by the hypothetical two-layer disk, virus assembly appears to be initiated by interaction of the specific RNA sequence with a short helical aggregate of the coat protein arranged as in the virus. Formation of the 20s nucleating aggregate involves the binding of an average of half a proton per protein subunit. This proton-binding site can be identified with the carboxyl-carboxylate pair that is formed between top and bottom protein surfaces at a radius of 58 A in the virus helix. Because the 20s aggregate consists of about two helical turns, only one carboxyl-carboxylate pair will be formed between each top-bottom pair of protein subunits. Limitation of the length of the 20s helical aggregate at neutral pH can be accounted for by disorder of the inner loop of the protein chain, due to electrostatic repulsion among the carboxyl groups that form the anomalous proton-binding site at 25 A radius in the ordered virus structure. To grow beyond two to three turns, inner loops of the protein at the interior of the helix must be ordered in the close-packed arrangement. The electrostatic repulsion opposing this ordering can be overcome by binding of the viral RNA at neutral pH, by calcium binding, or by proton binding in slightly acid solution. Virus disassembly upon infection appears to result from the low intracellular calcium and proton concentration compared to the extracellular environment, which increases the electrostatic repulsion among the negatively charged groups involved in calcium and proton binding, thereby allowing cellular ribosomes to competitively bind the viral RNA. Disk aggregates of TMV protein, which form at high ionic strength in alkaline solution, do not appear to be involved in virus assembly. The stacked-disc aggregate, which was previously presumed to be built of a polar stack of the hypothetical polar two-layer aggregate, is, in fact, a bipolar structure. Because the bonding between turns of the disc structures is different from that of the virus helix, direct switching between these structures by the postulated dislocation does not occur. TMV assembly does appear to involve conservation of bonding specificity, as initially presumed, but only in helical packing arrangements of the protein subunits. Switching from disordered to ordered conformations of the protein, dependent on changes in the electrostatic interactions among the protein subunits, appears to be critical in controlling the assembly process.

Microscopy, Electron↗

PubMed1992

Subunit assembly and posttranslational processing of Na(+)-pumps.

Assembly, posttranslational processing and intracellular transport of Na,K-ATPase subunits are closely linked processes. Only coexpression of alpha- and beta-subunits in Xenopus oocytes permits the structural maturation and the ER exit of the two subunits. A putative beta 3-isoform of Na,K-ATPase and the beta-subunit of H,K-ATPase can support similar functions to those of beta 1-subunits of Na,K-ATPase in allowing the functional expression of alpha-beta complexes with Na,K-pump transport properties in the plasma membrane. These data indicate that a primary role of the beta subunit is to impose a conformational change on the newly synthesized alpha-subunits probably involved in the acquisition of transport competence and functional maturity of the catalytic alpha-subunit.

Animals↗

PubMed1987

Spliceosome assembly in yeast.

Precursors to mRNA become substrates for splicing by being assembled into a complex multisubunit structure, the spliceosome. To study the assembly of the yeast spliceosome, intermediate complexes were separated by electrophoresis on nondenaturing polyacrylamide gels. Four splicing-dependent complexes, A1, A2-1, A2-2, and B, were observed. The order of assembly of these complexes was determined to be B----A2-1----A1----A2-2. The assembly process can be blocked at complex A1 by addition of 5 mM EDTA or by carrying out the assembly process in heat-inactivated rna2 extracts. The snRNA composition of the complexes was determined by hybridization with probes for five yeast snRNAs. snR14 (U4) was only found in complex A2-1, snR6 (U6) and snR7 (U5) were in complexes A1, A2-1, and A2-2, whereas snR20 (U2) was in all four of the complexes. snR19 (U1) was not present in any of the complexes. Hybridization with these probes was also employed to detect snRNPs present in yeast splicing extracts. We found that snR6, snR7, and snR14 were present together in a large complex. This complex underwent an ATP-dependent dissociation to give snR7 and snR6-snR14 complexes. snR19 and snR20 are present in distinct RNPs but the mobility of these is not affected by ATP. A mechanism for spliceosome assembly is proposed.

Animals↗

PubMed1991

Expression, processing, and assembly of foot-and-mouth disease virus capsid structures in heterologous systems: induction of a neutralizing antibody response in guinea pigs.

Plasmids containing the foot-and-mouth disease virus structural protein precursor (P1) and 3C protease genes or the P1 gene alone were expressed in Escherichia coli. A recombinant baculovirus containing the P1 gene was also generated and expressed in Spodoptera frugiperda cells. Expression of the P1 and 3C genes in E. coli resulted in efficient synthesis and processing of the structural protein precursor and assembly into 70S empty capsids. This material reacted with neutralizing monoclonal antibodies which recognize only conformational epitopes and elicited a significant neutralizing antibody response in vaccinated guinea pigs. Expression of the P1 gene in E. coli resulted in synthesis of an insoluble product, whereas in insect cells infected with the recombinant baculovirus a soluble product was synthesized. Both soluble and insoluble P1 reacted with a 12S-specific monoclonal antibody, but only soluble P1 elicited a neutralizing antibody response in guinea pigs.

Animals↗

PubMed1991

Mutational analysis of the mitochondrial Rieske iron-sulfur protein of Saccharomyces cerevisiae. III. Import, protease processing, and assembly into the cytochrome bc1 complex of iron-sulfur protein lacking the iron-sulfur cluster.

We have used site-directed mutagenesis of the Saccharomyces cerevisiae Rieske iron-sulfur protein gene (RIP 1) to convert cysteines 159, 164, 178, and 180 to serines, and to convert histidines 161 and 181 to arginines. These 4 cysteines and 2 histidines are conserved in all Rieske proteins sequenced to date, and 4 of these 6 residues are thought to ligate the iron-sulfur cluster to the apoprotein. We have also converted histidine 184 to arginine. This histidine is conserved only in respiring organisms. The site-directed mutations of the six fully conserved putative iron-sulfur cluster ligands result in an inactive iron-sulfur protein, lacking iron-sulfur cluster, and failure of the yeast to grow on nonfermentable carbon sources. In contrast, when histidine 184 is replaced by arginine, the iron-sulfur cluster is assembled properly and the yeast grow on nonfermentable carbon sources. The site-directed mutations of the 6 fully conserved residues do not prevent post-translational import of iron-sulfur protein precursor into mitochondria, nor do the mutations prevent processing of iron-sulfur protein precursor to mature size protein by mitochondrial proteases. Optical spectra of mitochondria from the six mutants indicate that cytochrome b is normal, in contrast to the deranged spectrum of cytochrome b which results when the iron-sulfur protein gene is deleted. In addition, mature size iron-sulfur apoprotein is associated with cytochrome bc1 complex purified from a site-directed mutant in which iron-sulfur cluster is not inserted. These results indicate that mature size iron-sulfur apoprotein, lacking iron-sulfur cluster, is inserted into the cytochrome bc1 complex, where it interacts with and preserves the optical properties of cytochrome b. Insertion of the iron-sulfur cluster is not an obligatory prerequisite to processing of the protein to its final size. Either the processing protease cannot distinguish between iron-sulfur protein with or without the iron-sulfur cluster, or insertion of the iron-sulfur cluster occurs after the protein is processed to its mature size, possibly after it is assembled in the cytochrome bc1 complex.

Amino Acid Sequence↗

PubMed1990

Inhibition of glycoprotein processing blocks assembly of spicules during development of the sea urchin embryo.

Previous studies have implicated an 130-kD glycoprotein containing complex, N-linked oligosaccharide chain(s) in the process of spicule formation in sea urchin embryos. To ascertain whether the processing of high mannose oligosaccharides to complex oligosaccharides is necessary for spiculogenesis, intact embryos and cultures of spicule-forming primary mesenchyme cells were treated with glycoprotein processing inhibitors. In both the embryonic and cell culture systems 1-deoxymannojirimycin (1-MMN) and, to a lesser extent, 1-deoxynojirimycin (1-DNJ) inhibited spicule formation. These inhibitors did not affect gastrulation in whole embryos or filopodial network formation in cell cultures. Swainsonine (SWSN) and castanospermine (CSTP) had no effect in either system. Further analysis revealed the following: (a) 1-MMN entered the embryos and blocked glycoprotein processing in the 24-h period before spicule formation as assessed by a twofold increase in endoglycosidase H sensitivity among newly synthesized glycoproteins upon addition of 1-MMN; (b) 1-MMN did not affect general protein synthesis until after its effects on spicule formation were observed; (c) Immunoblot analysis with an antibody directed towards the polypeptide chain of the 130-kD protein (mAb A3) demonstrated that 1-MMN did not affect the level of the polypeptide that is known to be synthesized just before spicule formation; (d) 1-MMN and 1-DNJ almost completely abolished (greater than 95%) the appearance of mAb 1223 reactive complex oligosaccharide moiety associated with the 130-kD glycoprotein; CSTP and SWSN had much less of an effect on expression of this epitope. These results indicate that the conversion of high mannose oligosaccharides to complex oligosaccharides is required for spiculogenesis in sea urchin embryos and they suggest that the 130-kD protein is one of these essential complex glycoproteins.

1-Deoxynojirimycin↗

PubMed1991

Expression, assembly, and processing of an active plant ferredoxin-NADP+ oxidoreductase and its precursor protein in Escherichia coli.

The flavoprotein ferredoxin-NADP+ reductase (FNR) catalyzes the final step of the photosynthetic electron transport chain, i.e. the reduction of NADP+ by ferredoxin. A cloned FNR cDNA from a pea library (Newman, B., and Gray, J. (1988) Plant Mol. Biol. 10, 511-520) was used to construct plasmids which express the apoenzyme in Escherichia coli. Two recombinant vectors were prepared, one containing the sequence corresponding to the mature enzyme and another including, in addition, the sequence of the transit peptide that directs FNR to the chloroplast. These proteins were expressed as fusion products to the NH2-terminal portion of beta-galactosidase. In both cases, a 35-kDa immunoreactive polypeptide was the major product, suggesting that the proteins were processed in vivo. NH2-terminal sequence determination of the purified recombinant proteins indicate cleavage at positions -1/-2 with respect to the normal processing site in chloroplasts. The processed enzymes showed enzymatic activities and spectral properties that were similar or identical to those of native plant FNR. When a La protease-deficient E. coli strain was used as a host, the expressed FNR precursor was found to be poorly processed, associated to bacterial pellets, and showed no detectable FNR activity. The overall results indicate that acquisition of the native enzyme conformation and assembly of the prosthetic group takes place in the bacterial host, generating an enzyme that is, as far as studied, indistinguishable from plant FNR.

Amino Acid Sequence↗

PubMed1984

Proteins of the kidney microvillar membrane. Effects of monensin, vinblastine, swainsonine and glucosamine on the processing and assembly of endopeptidase-24.11 and dipeptidyl peptidase IV in pig kidney slices.

The effects of various inhibitors were studied on the biogenesis of endopeptidase-24.11 (EC 3.4.24.11) and dipeptidyl peptidase IV (EC 3.4.14.5) in slices of renal cortex, from piglets of the Yucatan strain, maintained in organ culture. These microvillar peptidases were synthesized within membrane compartments and underwent glycosylation to yield high-mannose and complex forms [the preceding paper, Stewart & Kenny (1984) Biochem. J. 224, 549-558]. Monensin caused very gross ultrastructural changes in the proximal-tubular cells, resulting from distension of the Golgi sacs. It blocked the processing of the high-mannose to the complex glycosylated forms of the peptidases and prevented their assembly in the microvillar membrane. Swainsonine, an inhibitor of alpha-mannosidase II, generated new 'hybrid' forms of the proteins, intermediate in Mr between the high-mannose and the complex forms, but did not prevent assembly of the hybrid forms in microvilli. Vinblastine, an agent that affects microtubules, delayed, but did not abolish, either the processing or the transport to microvilli. Glucosamine interfered with the initial glycosylation reactions and generated heterogeneous sets of partially glycosylated polypeptides of lower Mr than the high-mannose forms. These results are discussed in relation to the site and mechanism of glycosylation and the involvement of the Golgi complex and microtubules in the biogenesis of these membrane peptidases.

Alkaloids↗

PubMed1991

Assembly of the Escherichia coli 30S ribosomal subunit reveals protein-dependent folding of the 16S rRNA domains.

Protein-nucleic acid interactions involved in the assembly process of the Escherichia coli 30S ribosomal subunit were quantitatively analyzed by high-resolution scanning transmission electron microscopy. The in vitro reconstituted ribonucleoprotein (core) particles were characterized by their morphology, mass, and radii of gyration. During the assembly of the 30S subunit, the 16S rRNA underwent significant conformational changes that were governed by the cooperative interactions of the ribosomal proteins. The sequential association of the first 12 proteins with the 16S rRNA resulted in the formation of core particles containing up to three mass centers at distinct stages of the assembly process. These globular mass centers may correspond to the three major domains (5', central, and 3') of the 16S rRNA. Through the subsequent interactions of the late assembly proteins with the 16S rRNA, two of the three domains merge, yielding the basic structural traits of the native 30S subunit. The fine morphological features of the native 30S subunit became distinctly resolved only after the addition of the full complement of proteins. The fully reconstituted 30S subunits are active in polyphenylalanine synthesis assays. Visualization of the assembly mechanism of the E. coli 30S ribosomal subunit revealed domain-specific folding of the 16S rRNA through the formation of distinct intermediate core particles hitherto not observed.

Bacterial Proteins↗

PubMed1991

Structure and assembly of the Escherichia coli transcription termination factor rho and its interactions with RNA. II. Physical chemical studies.

Transcription termination factor rho from Escherichia coli is comprised of a hexamer of identical protein monomers. Hydrodynamic and light-scattering studies have shown the fully assembled rho to be a doughnut-shaped structure. Semi-denaturing gels, protein crosslinking, and spectroscopic studies, as well as other functional and binding determinations have established that the rho hexamer displays D3 symmetry (i.e. it exists as a trimer of dimers). In the accompanying paper we visualize rho directly in the absence of cofactor and show that binding of RNA it into the hexameric form. In this paper we examine the pathway and association constants involved in rho oligomer assembly. Sedimentation and fluorescence-detected size exclusion chromatography are used to demonstrate three steps in the assembly process. These steps can be differentiated by subunit association affinity and kinetic properties. The kinetics of the monomer-dimer equilibrium are fast and an apparent association constant of 1.3 x 10(6) M-1 is measured for this process. In contrast, the dimer-tetramer and tetramer-hexamer association processes appear to be slower (of the order of seconds) and to involve association constants that are smaller than that of the monomer-dimer reaction. This behaviour is consistent with a hexamer of D3 symmetry. Such a particle displays two kinds of subunit interactions; one associated with an intra-dimer A:A interface and the other with an inter-dimer B:B interface. The closure of the circular hexamer does not appear to contribute additional free energy to the assembly process. Fluorescence and sedimentation studies show the association steps to be sensitive to salt concentration. Consistent with earlier work, we find that assembly to the hexameric state is driven by RNA binding.

Centrifugation, Density Gradient↗

PubMed1991

A Gly1 to Ala substitution in poliovirus capsid protein VP0 blocks its myristoylation and prevents viral assembly.

Capsid protein VP4 of poliovirus is acylated with myristic acid via an amide linkage to its N-terminal glycine residue. Our previous studies suggested that myristic acid plays a role in poliovirus assembly and in the early events of infection. In order to understand better its role in the assembly process, we introduced a Gly1 to Ala amino acid substitution in the myristoylation signal sequence of VP4. This substitution prevented VP0 myristoylation in vivo and abolished the infectivity of genomic transcripts harbouring the mutation. These mutated RNAs were still able to replicate in the transfected cells but the assembly processes were inefficient and no mature virions could be detected.

Alanine↗

PubMed1983

Evidence for the sequential assembly of cytochrome oxidase subunits in rat liver mitochondria.

The assembly of cytochrome oxidase was studied in isolated rat liver mitochondria and isolated rat hepatocytes labelled in vitro with L-[35S]methionine. This was achieved by studying the temporal association of radioactive subunits which are immunoabsorbed with antibodies against subunits I, II and the holoenzyme. Antibodies against the holoenzyme were shown to be highly specific for subunit V. The results show that subunit I appears in the holoenzyme late in the assembly process. No radioactive subunit I is absorbed with antiserum against subunit II or the holoenzyme (subunit V) after a 30 min pulse in either isolated mitochondria or hepatocytes. However, both antisera absorb radioactive subunits I after a 150 min chase in isolated hepatocytes. This was confirmed using antibodies against subunit I, which absorbed only radioactive subunit I after a 30 min pulse but absorbed radioactive subunits I-III and VI after a 150 min chase. Thus, the late assembly of radioactive subunit I is explained by a temporal sequence in the assembly process and not by the presence of a large, non-radioactive pool of subunit I. Using the above approach and the three specific antisera, the following temporal sequence in the assembly of cytochrome oxidase was established. Subunits II and III assemble rapidly with each other or with cytoplasmically translated subunit VI. This complex of three peptides in turn assembles slowly with subunit I or with the other cytoplasmically translated subunits. The early association of subunit VI with the mitochondrially translated subunits II and III suggests a possible role of the former in integration of the holoenzyme.

Animals↗

PubMed1985

Isolation of mutants in M13 coat protein that affect its synthesis, processing, and assembly into phage.

The major coat protein (gene 8 protein) of bacteriophage M13 has been studied intensively as a model of membrane assembly, protein packing, and protein-DNA interactions. Because this protein is essential for assembly of the phage, very few mutants have been isolated. We have therefore cloned the gene 8 into a plasmid under control of the araB promoter. In the presence of arabinose, the cloned gene is expressed at a rate comparable to that in an M13-infected cell. Plasmid-derived procoat is inserted across the plasma membrane and processed to coat at a normal rate. The coat can support plaque formation by a defective M13 virus (M13am8) with an amber mutation in its procoat gene. This complementation assay was used to screen the mutagenized, cloned gene 8 for mutants which fail to make fully functional coat. Mutants were obtained which fail to synthesize procoat, which do not convert procoat to mature coat protein, or in which the coat protein is incapable of assembling into infectious virions.

Arabinose↗

PubMed1978

Influence of toyocamycin on the assembly and processing of preribosomal ribonucleoproteins in the nucleolus of mammalian cells.

The adenosine analogue toyocamycin inhibits the maturation of ribosomal RNA, but permits the synthesis of other RNA species, including 45 S preribosomal RNA. In this work, the dose vs. response analysis of rRNA processing upon toyocamycin treatment of L5178Y cells is studied. It is shown that the latter steps of rRNA processing are more affected than the earlier. The mechanism responsible for the lack of conversion of toyocamycin-containing 45 S RNA into mature rRNA has not yet been elucidated. In order to investigate whether protein factors are involved in this mechanism, the effects of toyocamycin on the ability of preribosomal RNA to bind proteins and on the assembly of nucleolar preribosomes are investigated. The analogue allows the formation and the accumulation, in the nucleolus, of ribonucleoprotein complexes which contain 45 S RNA and newly synthesized proteins, but cannot be converted to mature ribosomal subunits. These complexes are not clearly distinguishable from 80 S particles synthesized in the absence of toyocamycin, with respect to their sedimentation rate in linear sucrose gradients, to their protein/RNA ratio and to their density measured in metrizamide gradients.

Antibiotics, Antineoplastic↗

PubMed1975

Applying concepts of visual perception to formats of hospital menus.

Standardized printed menu formats for all diets utilizing concepts of visual perception were evaluated in a machine-paced hospital tray-assembly process. Formats of existing menus differed among the various diets. On the redesigned menus, all menu items were arranged in basic groups which were assigned specific positions; groups were accentuated by white strips across the various color-coded selective menus; and accessory items were placed in specific, standard positions on all menus. Criteria for evaluating the effect of using the redesigned menu in tray assembly operations were: overall productivity, individual productivity, and error rate per tray. Data were charted (a) during a control period when the existing menu formats were used to provide baseline data and (b) during an experimental period when the redesigned menu formats were used. Overall productivity was measured by man-minutes per tray. Video tapes of five station operators servicing selected trays were made to study individual productivity. Station operator and checker accuracy were measured in terms of ratio of error-free trays, errors per tray, and errors to possibility of errors per tray. Man-minutes per tray decreased significantly in the experimental period from 2.44 to 2.17--a productivity increase of 11.1 per cent. The individual productivity analysis revealed no significant changes from control to experimental periods. Accuracy of the tray assembly station operators improved significantly. Decreases in ratio of mean number of errors to possibility of errors per tray were recorded in the experimental period. The error rate per tray decreased 44.9 per cent from 0.48 to 0.26, and the ratio of errors to possibility of errors per tray decreased from 6.3 to 3.5 per cent. The percentage of error-free trays rose from 69.9 to 80.9 per cent. Checkers' errors per tray did not change significantly from control to experimental period when data for the two periods were compared. This study provides a practical means of increasing productivity and improving accuracy of the machine-paced tray assembly process.

Audiovisual Aids↗