Rate Of Total Protein Synthesis Research Articles

3H]proline incorporation and hydroxyproline concentration in articular cartilage during the development of osteoarthritis caused by immobilization. A study in vivo with rabbits.

Proline metabolism in vivo was studied during the development of immobilization osteoarthritis in rabbits. Collagen content was measured as the hydroxyproline concentration of the tissue in question. The incorporation of [3H]proline was used as the indicator for total protein synthesis; collagen synthesis rate was estimated from measurements of the specific radioactivity of hydroxyproline. Cartilage samples from knee and hip joints were analysed after 3, 7, 11, 18, 35 and 56 days of immobilization. The total protein and collagen synthesis rates of the immobilized legs increased and reached a maximum after 11-35 days. Although they decreased thereafter, these rates remained elevated to the end of the experiment. A slight increase in the synthetic activity of the non-immobilized contralateral legs was also detected after 7--18 days of immobilization. The isotope incorporation was markedly higher in tibial marginal tissue than in weight-bearing cartilage. In spite of the increased synthesis, no clear changes were found in the collagen content of the tissues studied during the experiment.

Effects of plating density and age in culture on growth and cell division of neonatal rat heart primary cultures.

The cell-type composition of the initial cell population from protease-dispersed neonatal rat heart tissue has been evaluated using time lapse photography and identification of cell type-specific functions. The effects of two commonly employed plating densities on growth and cell division of the two major cell types were examined. Total protein synthesis rates were not affected by plating density but did change with age in culture. Maximum protein synthesis rates were observed during the period of maximum cell division and cell growth (increase in total cell protein), which was from 24 h in culture to the 4th d in culture. After 6 d in culture, synthesis rates for total proteins remained constant for at least 2 wk. Sizing of cells by Coulter counter analysis indicated that essentially all the cells were increasing in size with age in culture.

A procedure for measuring the contributions of intracellular and extracellular tyrosine pools to the rate of myocardial protein synthesis

To determine the relative contribution of intracellular and extracellular amino acid sources as precursors for protein synthesis, rat left atria were incubated in l-[ 3H]tyrosine at medium tyrosine concentrations ranging from 0.05 to 2.5 m m. Under conditions where protein synthesis was shown to be constant, tyrosine incorporation rates calculated from either the intracellular or extracellular tyrosine concentration. This behavior is consistent with a model which postulates that amino acids inside and outside the cell simultaneously supply a common precursor pool. A method is presented for determining the contributions of the intracellular and extracellular pools to the total protein synthesis rate. Analysis of tyrosine incorporation data according to this procedure yields a total incorporation rate of 1.14 ± 0.18 ( s.e.m.) nmol tyrosine/mg protein/h, of which 61 ± 15% is attributed to a mixed intracellular source and 39 ± 7% to amino acids taken directly from the extracellular medium. During a 3-h incubation of the isolated atria protein synthesis and degradation rates were equal, and the oxygen consumption and ATP and creatine phosphate levels were similar to those of the beating, perfused heart.

Growth-rate-dependent regulation of ribosome synthesis in E. coli: Expression of the lacZ and galK genes fused to ribosomal promoters

Hybrid transducing phages were constructed in vitro that carry the galK gene fused to each of three ribosomal promoters: the promoter for an rRNA operon ( rrnE); the promoter for the spc r protein operon; and the promoter for the α r protein operon. We also constructed hybrid transducing phages that carry the lacZ gene fused to the promoter for the rrnE operon or to the promoter for the spc r protein operon. The amounts of galactokinase (or β-galactosidase) were analyzed in lysogens carrying these various transducing phages grown in several different growth media. The synthesis rate of galactokinase (or β-galactosidase) from the fused rrn-gal (or rrn-lac) operon relative to the total protein synthesis rate increased with increasing growth rate, as expected from the transcriptional activity of rRNA operons. In contrast, the relative synthesis rate of galactokinase (or β-galactosidase) from the operon fused to α or spc r protein promoter remained approximately constant with increasing growth rate. These results were interpreted to mean that the characteristic increase in the relative synthesis rate of r protein with increasing growth rate is determined not by transcriptional regulatory mechanisms, but by posttranscriptional mechanisms, which presumably involve the feedback inhibition of r protein mRNA translation by free r proteins.

Whole body protein synthesis and turnover in normal man and malnourished patients with and without known cancer.

Plateau enrichment of 15N-ammonia following 24 hour continuous intravenous infusion of 15N-glycine was used to measure total body protein turnover and synthesis in normal volunteers and malnourished patients, with and without cancer. The mean postabsorptive total body protein synthesis rate in three normal controls was 2.5 g protein/kg/day. Protein synthesis and turnover decreased by a mean of 23% following one week of fasting, and returned to baseline levels following one week of refeeding. In three malnourished patients without known tumor, whole body protein synthesis and turnover was similar to controls; following seven to ten days of total parenteral nutrition (TPN) in the nontumor-bearing patients whole body protein synthesis and turnover decreased by 18%. Three of seven malnourished patients with known tumors had marked elevations in total body protein synthesis and turnover; TPN increased protein turnover in five of seven patients with known cancer. This study suggests that some malignant tumors can increase whole body protein synthesis and turnover in both the malnourished and fed state. This increase in protein turnover may represent a direct effect of the tumor, or reflect concomitant illness.

Rates of ribosomal protein and total protein synthesis during Drosophila early embryogenesis

Embryos at various stages of early development from 1.5 to 5 hr after oviposition were made permeable with octane and labeled for 1 hr with [ 3H]phenylalanine. Measurements of the rate of incorporation of [ 3H]phenylalanine into ribosomal proteins and total protein were made using these synchronized Drosophila embryos. The rate of synthesis of those ribosomal proteins incorporated into ribosomes increases until 3 to 4 hr after fertilization (550 pg/embryo-hr) then declines later in embryonic development. The rate of total protein synthesis is maximal as early during embryonic development as could be measured. During the period between 1.5 and 2.5 hr after fertilization this rate is 9.4 ng/embryo-hr and then also declines. The synthesis of ribosomal proteins accounts for a substantial portion (4.5%–8.9%) of total protein synthesis in early embryos. These results indicate that ribosome formation is a significant activity during the earliest stages of Drosophila development.

Program of early development in the mammal: Synthesis and intracellular migration of histone H4 during oogenesis in the mouse

Synthesis of histone H4 by mouse oocytes and unfertilized eggs has been examined by using a modified high-resolution two-dimensional gel electrophoresis procedure capable of resolving basic proteins (M. J. LaMarca and P. M. Wassarman, 1979, Develop. Biol. 73, 103–119) . Histones were separated on such gels and observed rates of incorporation of [ 35S]methionine into histone H4 were converted into absolute rates of synthesis by using previously determined values for the absolute rates of total protein synthesis in mouse oocytes and unfertilized eggs (R. M. Schultz, G. E. Letourneau, and P. M. Wassarman, 1979, Develop. Biol. 68, 341–359; 73, 120–133) . Histone H4 was synthesized at all stages of oogenesis examined, and accounted for 0.07, 0.05, and 0.04% of total protein synthesis in growing oocytes, fully grown oocytes, and unfertilized eggs, respectively. During oocyte maturation the absolute rate of histone H4 synthesis decreased by about 40%, as compared to a 23% decrease in the rate of total protein synthesis during the same period. These measurements indicate that enough histone is synthesized during oogenesis in the mouse to support two to three cell divisions. Examination of the intracellular location of newly synthesized proteins in fully grown oocytes revealed that histone H4 was highly concentrated in the nucleus (germinal vesicle), whereas total protein and tubulin were not. Nearly 50% of the histone H4 synthesized during a 5-hr period was located in the oocyte's germinal vesicle, as compared to 1.9 and 0.9% for total protein and tubulin, respectively. These results are compared with those obtained using oocytes and eggs from nonmammalian animal species.

CYTOSKELETAL STRUCTURES MAY LINK CHOLESTEROL SYNTHESIS TO GLIAL DIFFERENTIATION

Cholesterol synthesis is a highly critical process in developing brain, particularly in glia, because cholesterol is a major constituent of all cellular membranes, including myelin. We have shown recently that the rate limiting enzyme in cholesterol biosynthesis, HMG-CoA reductase (HMG-R), is actively regulated in cultured C-6 glial cells, a model of the differentiating glial cell, and that this regulation involves microtubules. This study elucidates further the role of cytoskeletal structures. Microfilaments were disrupted by exposure of the cells to cytochalasin D (cD). Within 1 h of the addition of 1 μM cD, there resulted a 50% reduction in HMG-R activity, and after 3 h an 80% reduction. A decrease of 50% occurred with just 0.2 μM cD (3 h). The effects were fully reversible. The specificity of the effect was indicated by the findings of no change in the activities of five other critical glial enzymes or in the rate of total protein synthesis. That the decrease in HMG-R activity caused by cD is related to a decrease in enzyme content was suggested by the observation that cycloheximide blocked the recovery of activity after removal of cD. A relation of the effect of cD on reductase to disruption of microfilaments was suggested by striking concomitant morphological changes caused by the drug. Coupled with our previous findings, the observations suggest a link between a microfilament-microtubular system and both glial differentiation and cholesterol biosynthesis. Such a link would be of major neurobiological importance because it would provide a mechanism for coupling membrane biogenesis to cellular differentiation. (Supported by NIH grant R01 HD-07464).

Translational control of protein synthesis after infection by vesicular stomatitis virus.

Four hours after infection of BHK cells by vesicular stomatitis virus (VSV), the rate of total protein synthesis was about 65% that of uninfected cells and synthesis of the 12 to 15 predominant cellular polypeptides was reduced to a level about 25% that of control cells. As determined by in vitro translation of isolated RNA and both one- and two-dimensional gel analyses of the products, all predominant cellular mRNA's remained intact and translatable after infection. The total amount of translatable mRNA per cell increased about threefold after infection; this additional mRNA directed synthesis of the five VSV structural proteins. To determine the subcellular localization of cellular and viral mRNA before and after infection, RNA from various sizes of polysomes and nonpolysomal ribonucleoproteins (RNPs) was isolated from infected and noninfected cells and translated in vitro. Over 80% of most predominant species of cellular mRNA was bound to polysomes in control cells, and over 60% was bound in infected cells. Only 2 of the 12 predominant species of translatable cellular mRNA's were localized to the RNP fraction, both in infected and in uninfected cells. The average size of polysomes translating individual cellular mRNA's was reduced about two- to threefold after infection. For example, in uninfected cells, actin (molecular weight 42,000) mRNA was found predominantly on polysomes with 12 ribosomes; after infection it was found on polysomes with five ribosomes, the same size of polysomes that were translating VSV N (molecular weight 52,000) and M (molecular weight 35,000) mRNA. We conclude that the inhibition of cellular protein synthesis after VSV infection is due, in large measure, to competition for ribosomes by a large excess of viral mRNA. The efficiency of initiation of translation on cellular and viral mRNA's is about the same in infected cells; cellular ribosomes are simply distributed among more mRNA's than are present in growing cells. About 20 to 30% of each of the predominant cellular and viral mRNA's were present in RNP particles in infected cells and were presumably inactive in protein synthesis. There was no preferential sequestration of cellular or viral mRNA's in RNPs after infection.

Measurement of the synthesis rates of collagens and total protein in rabbit muscle.

1. Collagen- and total-protein-synthesis rates were determined in rabbit muscle by continuous infusion of radioactive proline. 2. The precursor pool of free proline used for collagen synthesis was defined by measuring the specific radioactivity of hydroxy-proline in isolated type I procollagen. The specific radioactivities of type I procollagen were about 40% of those for free proline in the homogenate. 3. The mean ratio (+/- S.E.M.) between the fractional synthesis rates of muscle collagen and total protein was 0.99 +/- 0.10, where the total protein values were based on specific radioactivities of the homogenate free proline pools. 4. Types I, III and V collagen were solubilized by pepsin and isolated by fractional precipitation with NaCl. The fractional synthesis rates of types I and III collagens were very similar. Type V collagen samples had higher specific radioactivities than the other collagens, but this was not necessarily indicative of a higher rate of synthesis because of uncertainty about the cellular origin of this collagen and, hence, the specific radioactivity of its precursor proline pool.

Enhanced synthesis of collagen and total protein by smooth muscle cells from atherosclerotic rabbit aortas in culture

Protein synthesis in smooth muscle cells from normal and atherosclerotic rabbit aortas was studied. Cultures of cells from the third passage were incubated with [ 3H]proline and the synthesis rates of collagen and total protein measured from the radioactivities incorporated into protein-bound hydroxyproline pro proline, respectively. The synthesis ratio of collagen types I and III was studied by separating the radioactive procollagens of the culture media by DEAE column chromatography. The synthesis rates of both collagen and total protein were higher in cells cultured from atherosclerotic rabbit aortas. There was no difference in the synthesis ratios of types I and III collagen between cells from the two origins. In addition to procollagens, a third protein eluted before procollagen I in the DEAE chromatography of medium proteins. Compared with control cells, cells from atherosclerotic aortas incorporated relatively less radioactivity into this protein. No differences were detected in the amino acid compositions of cellular proteins between cells from both origins. It was concluded that cells grown from atherosclerotic rabbit aortas synthesize more collagen and total protein than those from normal aortas, the synthesis of collagens I and III being equally enhanced. The results also suggest that there are proteins which are not involved in the general enhancement of protein synthesis.

Ozone-induced alterations in collagen metabolism of rat lungs: II. Long-term exposures

Rats were exposed to 0.5 ppm of ozone delivered for 23.5 hr per day for up to 180 days. One group of rats was allowed to breathe filtered air for about 2 months after the conclusion of the exposure. Lung collagen and total-protein synthesis rates were quantitated by biochemical analyses performed with lung minces. Other lung lobes from the same rats were used to quantitate collagen and total protein content. Increased levels of lung protein and of lung collagen (hydroxyproline) content were observed at all times sampled during exposure to ozone (3, 30, 50, 88, 180 days); the observed lung hydroxyproline content at 180 days persisted during the 2 months of postexposure recovery. Collagen synthesis rates measured in lung minces were elevated in the exposed rats at all times sampled, consistent with the observed increased lung collagen content seen throughout the study. The observed biochemical changes were consistent with concurrent morphological observations of the occurrence of mild pulmonary fibrosis.

Whole body protein turnover, studied with 15N-glycine, and muscle protein breakdown in mildly obese subjects during a protein-sparing diet and a brief total fast

A modification of the Picou and Taylor-Roberts Model was used to estimate rates of total body protein synthesis (S), breakdown (C), and amino nitrogen (N) flux (Q) in the metabolic N pool of five obese females. The subjects were fed egg white albumin at 1.5/kg ideal body weight (IBW) and total calories at 1.2 times the basal energy expenditure (fat:carbohydrate = 30%:50%) as a formula diet (period 1, 1 wk). This was followed by 3 wk during which the nonprotein calories were omitted (period 2, protein-sparing modified fast [PSMF]) and a 1-wk total fast (period 3). Estimates of body protein turnover and skeletal protein breakdown were made during the last 60 and 48 hr, respectively, of each period. Q, S, and C were 223 ± 22, 154 ± 22, and 150 ± 22 g protein 24 hr , respectively, for period 1. These values were unchanged at the end of period 2. Total fasting decreased Q and S by 36% and 27%, respectively ( p < 0.001), but C remained unchanged. Skeletal protein breakdown, as estimated by urinary Nτ-methylhistidine excretion, was 108 ± 47 μmole in period 1, 79 ± 51 μmole in period 2 ( p < 0.01), and 100 ± 49 μmole in period 3, representing 16 ± 5%, 12 ± 5% ( p < 0.01), and 16 ± 4% of whole body breakdown. N balance was unchanged in period 1 (−0.4 ± 1.2 g N) and the final week of period 2 (−0.4 ± 1.5 g N), but was −5.8 ± 0.6 g N in period 3. These data indicate that weight reduction with a PSMF is associated with a maintenance of total body protein turnover parameters and N balance but a reduction in skeletal protein breakdown, whereas a total fast causes a marked reduction in whole body protein synthesis and amino N flux with little change in the rate of total body and skeletal protein breakdown, resulting in a negative N balance. The minimization of N losses that develops after prolonged starvation is achieved at rates of whole body and skeletal protein breakdown similar to those found when the diet is adequate, suggesting that endogenous fat-derived fuels are as effective as exogenous energy in limiting protein catabolism. However, protein intake is necessary to maintain whole body protein synthesis under these conditions.

Induction of fatty acid synthetase synthesis in differentiating 3T3-L1 preadipocytes.

3T3-L1 preadipocytes, cloned from 3T3 mouse embryo fibroblasts, differentiate in monolayer culture into cells with morphological and biochemical characteristics of adipocytes. Deposition of cytoplasmic triglyceride is associated with an increased lipogenic rate and a coordinate rise in the activities of many lipogenic enzymes (Mackall, J.C., Student, A.K., Polakis, S.E., and Lane, M.D. (1976) J. Biol. Chem. 251, 6462-6464). During differentiation induced by a 48-h treatment of postconfluent cells with methylisobutylxanthine, dexamethasone, and insulin, fatty acid synthetase activity increased to a level 19.5-fold higher than that of undifferentiated 3T3-L1 cells or nondifferentiating 3T3-C2 cells. The rate of [3H]leucine incorporation into immunoadsorbable fatty acid synthetase rose to a maximum and then declined to a new level 12.5-fold higher in differentiated than in undifferentiated 3T3-L1 cells. The kinetics of the changing [3H]leucine incorporation rate was reflected in the kinetics of the rise in fatty acid synthetase activity. The rate of degradation of fatty acid synthetase, determined by pulse-chase experiments, was unaffected by differentiation, the t1/2 remaining constant at 1.4 days. It is concluded that the higher level of fatty acid synthetase activity in differentiated 3T3-L1 cells can be attributed entirely to an increased rate of enzyme synthesis. The rate of total cellular protein synthesis also increases early early in differentiation, lending support to a model in which the synthesis of a large number of "differentiated proteins" is coordinately induced.

Direct effects of rat growth hormone in rat islets of langerhans in tissues culture.

The effects of rat growth hormone (1 microgram/ml) on the synthesis and release of insulin by isolated rat islets of Langerhans were studied. There was no effect of growth hormone on the release of insulin from freshly isolated islets during 30 min incubation periods. By contrast, islets previously cultured for 16h with growth hormone exhibited at 40% increase in the release of insulin in response to glucose or to glucose and theophylline. These islets also showed specific increases in basal and glucose-stimulated insulin synthesis of 16% and 21% respectively, together with a 22% increase in the basal rate of total protein synthesis. The total insulin content of islets was not affected by culture with growth hormone. The adenylate cyclase activity of islet homogenates was unaffected by the presence of growth hormone during 30 min incubations. When homogenates from islets previously cultured with growth hormone were studied, basal adenylate cyclase activity was unchanged, while fluoride-stimulated adenylate cyclase activity was increased by 37%. It is concluded that growth hormone can directly affect the synthesis and release of insulin in islets of Langerhans, without relation to its metabolic activities in other target organs.

The synthesis and distribution of desmin and vimentin during myogenesis in vitro

Electrophoretic and autoradiographic analyses of the incorporation of 35S-methionine into newly synthesized proteins during myogenesis reveal that presumptive chicken myoblasts synthesize primarily one intermediate filament protein: vimentin. Desmin synthesis is initiated at the onset of fusion. Synthesis rates of both filament subunits increase during the first three days in culture, relative to the total protein synthesis rate. The observed increase in the rate of desmin synthesis (at least 10 fold) is significantly greater than that observed for vimentin, and is responsible for a net increase in the cellular desmin content relative to vimentin. Both filament subunits continue to be synthesized through at least 20 days in culture. Immunofluorescent staining using desmin- and vimentin-specific antisera supports the conclusion that desmin is synthesized only in fusing or multinucleate cells. These results indicate that the synthesis of the two filament subunits is not coordinately regulated during myogenesis. The distributions of desmin and vimentin in multinucleate chicken myotubes are indistinguishable, as determined by double immunofluorescence techniques. In early myotubes, both proteins are found in an intricate network of free cytoplasmic filaments. Later in myogenesis, several days after the appearance of α-actinin-containing Z line striations, both filament proteins become associated with the Z lines of newly assembled myofibrils, with a corresponding decrease in the number of cytoplasmic filaments. This transition corresponds to the time when the a-actinin-containing Z lines become aligned laterally. These data suggest that the two intermediate filament systems, desmin and vimentin, have an important role in the lateral organization and registration of myofibrils and that the synthesis of desmin and assembly of desmin-containing intermediate filaments during myogenesis is directly related to these functions. These results also indicate that the Z disc is assembled in at least two distinct steps during myogenesis.

A kinetic model of protein synthesis. Application to hemoglobin synthesis and translational control.

We present a kinetic model of protein synthesis which encompasses initiation, elongation, and termination parameters. We have investigated the dependence of the total rate of protein synthesis and the size of the translating polysomes on each of these parameters and in particular on the level of active 40 S ribosomes and initiation factors. This model qualitatively fits experimental data for the ratio of alpha- to beta-globin synthesis in reticulocytes, both under normal conditions and in the presence of inhibitors of chain initiation. This model has also been used to examine the effect that limiting amounts of certain tRNAs might have on the total rate of protein synthesis. In addition, the role of initiation factor discrimination and mRNA length are examined with respect to the differential translation of mRNAs.

Effects of gibberellic acid and of tunicamycin on glycosyl-transferase activities and on alpha-amylase secretion in barley.

A crude membrane fraction was prepared from isolated aleurone layers, the secretory tissue of barley grains. The layers were pre-incubated in the presence or absence of the phytohormone gibberellic acid. The membranes catalyzed the transfer of [14C]mannose from GDP-[14C]mannose and of N-[14C]acetylglucosamine from UDP-N-[14C]acetylglucosamine to endogenous and exogenous dolichyl monophosphate. When gibberellic acid was present during the pretreatment the activity of the transferases was increased by a factor of two to three. A significantly increased activity was observable within four hours after the addition of gibberellic acid, whereas the gibberellic-acid-induced secretion of the glycoprotein alpha-amylase started only after 12 h. Tunicamycin inhibited the secretion of alpha-amylase by 60 to 80%. Intracellularly, however, no alpha-amylase was found to accumulate. On the other hand, tunicamycin did not inhibit the rate of total protein synthesis by more than 10%. The possibility is discussed that the synthesis of the protein portion of glycoproteins is specifically inhibited, when glycosylation is prevented.

Program of early development in the mammal: Changes in the patterns and absolute rates of tubulin and total protein synthesis during oocyte growth in the mouse

Oocytes at several stages of growth have been isolated by enzymatic digestion and/or physical disruption of ovaries excised from juvenile and adult mice. The absolute rates of total protein synthesis and tubulin synthesis in these isolated oocytes were determined by measuring sizes of the endogenous methionine pool and apparent rates of incorporation of [ 35S]methionine into total protein and tubulin using methods described previously ( R. M. Schultz, M. J. LaMarca, and P. M. Wassarman, 1978, Proc. Nat. Acad. Sci. USA, 75, 4160; R. M. Schultz, G. E. Letourneau, and P. M. Wassarman, 1979, Develop. Biol., 68, 341). The size of the endogenous methionine pool increases approximately 350-fold during oocyte growth, from 0.16 fmole in nongrowing oocytes (12 μm) to 56 fmole in fully grown oocytes (85 μm). Since the volume of mouse oocytes also increases about 350-fold during growth, the concentration of intracellular free methionine remains constant at approximately 170 μ M. The absolute rate of protein synthesis increases from 1.1 to 41.8 pg/hr/oocyte for nongrowing and fully grown mouse oocytes, respectively. Since this represents about a 38-fold increase in the absolute rate of protein synthesis, the rate of synthesis per picoliter of cytoplasm actually decreases nearly 10-fold during oocyte growth. These measurements indicate that the growing mouse oocyte itself is capable of synthesizing only about 50% of the protein found in fully grown oocytes. Tubulin is one of the major proteins synthesized by growing mouse oocytes since the absolute rate of tubulin synthesis is, on the average, 1.8% of total protein synthesis. The absolute rate of tubulin synthesis increases from 0.4 to 0.6 pg/hr/oocyte as the oocyte grows from 40 to 85 μm in diameter. However, overall, the percentage of total protein synthesis devoted to the synthesis of tubulin actually declines somewhat during this phase of growth, from 2 to 1.5%. Although equimolar amounts of tubulin subunits are present in microtubules, the ratio of absolute rate of synthesis of the β subunit to that of the α subunit varies from 1.3 to 2.0 throughout oocyte growth. High-resolution two-dimensional gel electrophoretic analyses of [ 35S]methionine-labeled proteins reveal that many changes take place in the pattern of protein synthesis during oocyte growth.

Program of early development in the mammal: Changes in absolute rates of synthesis of ribosomal proteins during oogenesis and early embryogenesis in the mouse

The absolute rates of synthesis of specific ribosomal proteins have been determined during growth and meiotic maturation of mouse oocytes, as well as during early embryogenesis in the mouse. These measurements were made possible by the development of a high-resolution twodimensional gel electrophoresis procedure capable of resolving basic proteins with isoelectric points between 9.1 and 10.2. Mouse ribosomal proteins were separated on such gels and observed rates of incorporation of [ 35S]methionine into each of 12 representative ribosomal proteins were converted into absolute rates of synthesis (femtograms or moles synthesized/hour/oocyte or embryo) by using previously determined values for the absolute rates of total protein synthesis in mouse oocytes and embryos ( R. M. Schultz, M. J. LaMarca, and P. M. Wassarman, 1978, Proc. Nat. Acad. Sci. USA, 75, 4160; R. M. Schultz, G. E. Letourneau, and P. M. Wassarman, 1979, Develop. Biol., 68, 341–359). Ribosomal proteins were synthesized at all stages of oogenesis and early embryogenesis examined and, while equimolar amounts of ribosomal proteins were found in ribosomes, they were always synthesized in nonequimolar amounts during development. Rates of synthesis of individual ribosomal proteins differed from each other by more than an order of magnitude in some cases. Synthesis of ribosomal proteins accounted for 1.5, 1.5, and 1.1% of total protein synthesis during growth of the oocyte, in the fully grown oocyte, and in the unfertilized egg, respectively. During meiotic maturation of mouse oocytes the absolute rate of synthesis of ribosomal proteins decreased about 40%, from 620 to 370 fg/hr/cell, as compared to a 23% decrease in the rate of total protein synthesis during the same period. On the other hand, during early embryogenesis the absolute rates of synthesis of each of the 12 ribosomal proteins examined increased substantially as compared with those of the unfertilized egg, such that at the eight-cell stage of embryogenesis synthesis of ribosomal proteins (4.17 pg/hr/embryo) accounted for about 8.1% of the total protein synthesis in the embryo. Consequently, while the absolute rate of total protein synthesis increased about 1.5-fold during development from an unfertilized mouse egg to an eight-cell compacted embryo, the absolute rate of ribosomal protein synthesis increased more than 11-fold during the same period. These results seem to reflect the differences reported for the patterns of ribosomal RNA synthesis during early development of mammalian, as compared to nonmammalian, animal species. The results are compared with those obtained using oocytes and embryos from Xenopus laevis.