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Respirovirus C protein blocks the type I interferon (IFN)-stimulated activation of the JAK-STAT pathway. It has been reported that C protein inhibits IFN-α-stimulated tyrosine phosphorylation of STATs, but the underlying mechanism is poorly understood. Here, we show that the C protein of Sendai virus (SeV), a member of the Respirovirus genus, binds to the IFN receptor subunit IFN-α/β receptor subunit (IFNAR)2 and inhibits IFN-α-stimulated tyrosine phosphorylation of the upstream receptor-associated kinases, JAK1 and TYK2. Analysis of various SeV C mutant (Cm) proteins demonstrates the importance of the inhibitory effect on receptor-associated kinase phosphorylation for blockade of JAK-STAT signaling. Furthermore, this inhibitory effect and the IFNAR2 binding capacity are observed for all the respirovirus C proteins examined. Our results suggest that respirovirus C protein inhibits activation of the receptor-associated kinases JAK1 and TYK2 possibly through interaction with IFNAR2.

The 11 kDa, positively charged dengue capsid protein (C protein) exists stably as a homodimer and colocalizes with the viral genome within mature viral particles. Its core is composed of four alpha helices encompassing a small hydrophobic patch that may interact with lipids, but approximately 20% of the protein at the N-terminus is intrinsically disordered, making it challenging to elucidate its conformational landscape. Here, we combine small-angle X-ray scattering (SAXS), amide hydrogen-deuterium exchange mass spectrometry (HDXMS), and atomic-resolution molecular dynamics (MD) simulations to probe the dynamics of dengue C proteins. We show that the use of MD force fields (FFs) optimized for intrinsically disordered proteins (IDPs) is necessary to capture their conformational landscape and validate the computationally generated ensembles with reference to SAXS and HDXMS data. Representative ensembles of the C protein dimer are characterized by alternating, clamp-like exposure and occlusion of the internal hydrophobic patch, as well as by residual helical structure at the disordered N-terminus previously identified as a potential source of autoinhibition. Such dynamics are likely to determine the multifunctionality of the C protein during the flavivirus life cycle and hence impact the design of novel antiviral compounds.

Background: Ixora coccinea is a tropical ornamental shrub employed in ethnomedicine for the treatment of a number of diseases none of which include the Human Immunodeficiency Virus (HIV) infection. Ixoratannin A-2, one of the constituents, was previously identified via virtual-screening and experimentally confirmed to possess significant anti-HIV-1 activity in an in vitro CD4+ replication assay. This activity was observed to be significantly reduced in degree in viruses lacking the protein Vpu. This suggests the involvement of Vpu as well as other extra-Vpu macromolecules in its antiviral activity. Methods: In the present computational search for the identity of the other macromolecules that could possibly explain the observed activity, a panel of fourteen established HIV-1 macromolecular targets was assembled against which ixoratannin A-2 and other major phytoconstituents of I. coccinea were virtually screened. Results: Structural analyses of the computed ligand-bound complexes, as well as the careful investigation of the thermodynamic attributes of the predicted binding, revealed subtle selectivity patterns at the atomistic level that suggest the likely involvement of multiple macromolecular processes. Some of the binding interactions were found to be thermodynamically favourable, including the multidrug-resistant HIV protease enzyme, CXCR4 and the human elongin C protein all of which formed reasonably strong interactions with ixoratannin A-2 and other constituents of I. coccinea. Conclusion: Ixoratannin A-2’s ability to favourably interact with multiple HIV-1 and human targets could explain its observed extra-Vpu antiviral activity. This, however, does not imply uncontrolled binding with all available targets; on the other hand, molecular size of ixoratannin A-2 and combination of functional groups confer on it a decent level of selectivity against many of the investigated HIV/AIDS targets.

Measles virus (MV) C protein has been known a multifunctional protein involved in anti-IFN response, viral RNA synthesis, and so on. Recent studies have clarified that double-stranded RNA (dsRNA) is derived from viral genomic RNA (vRNA), and the amount of dsRNA was increased in an MV lacking C protein (MV(C-))-infected cells, suggesting that C protein blocks viral RNA synthesis. However, detailed roles of C protein in viral RNA synthesis remain unknown. Here, we have confirmed through time course experiments using Vero/hSLAM cells that as reported previously, the amount of mRNA is increased in MV(C-)-infected cells at 36 h post infection (hpi). In contrast, we found that the transcription level is lower in MV(C-)-infected cells than wild-type MV-infected cells in early phases of infection. Immunoprecipitation assays were performed to find an interactor(s) of C protein, revealed that C protein interacts with N protein in the absence of vRNA and P protein. RNA immunoprecipitation (RIP) assays showed that the interaction between N protein and vRNA was increased in MV(C-)-infected cells. These results suggest that in early phases of infection C protein facilitates viral transcription to control the formation of nascent nucleocapsid composed of N protein and vRNA.

Paramyxovirus C protein targets the host interferon (IFN) system for virus immune evasion. To identify its unknown anti-IFN activity, we examined the effect of Sendai virus C protein on activation of the IFN-α promoter via various signaling pathways. This study uncovers a novel ability of C protein to block Toll-like receptor (TLR) 7- and TLR9-dependent IFN-α induction, which is specific to plasmacytoid dendritic cells. C protein interacts with a serine/threonine kinase IKKα and inhibits phosphorylation of IRF7. This anti-IFN activity of C protein is shared across genera of the Paramyxovirinae, and thus appears to play an important role in paramyxovirus immune evasion.

Standard genetic approaches allow the production of protein composites by fusion of polypeptides in head-to-tail fashion. Some applications would benefit from constructions that are genetically impossible, such as the site-specific linkage of proteins via their N or C termini, when a remaining free terminus is required for biological activity. We developed a method for the production of N-to-N and C-to-C dimers, with full retention of the biological activity of both fusion partners and without inflicting chemical damage on the proteins to be joined. We use sortase A to install on the N or C terminus of proteins of interest the requisite modifications to execute a strain-promoted copper-free cycloaddition and show that the ensuing ligation proceeds efficiently. Applied here to protein–protein fusions, the method reported can be extended to connecting proteins with any entity of interest.

A comparative study was made of the extent of phosphorylation of myosin regulatory light chains and C-protein from the left ventricle of the hibernant ground squirrel Citellus undulatus during the periods of hibernation and activity. During hibernation, the light chains were found to be completely dephosphorylated. In active animals, the share of phosphorylated light chains averaged 40–45%. The extent of cardiac C-protein phosphorylation in hibernation was about twice higher than in the active state. Seasonal differences in phosphorylation of the two proteins of ground squirrel myocardium are discussed in the context of adaptation to hibernation.

Sendai virus C protein interacts with the signal transducer and activator of transcription (STAT) 1. This interaction is believed to be essential for the Sendai virus inhibition of the interferon (IFN) response. We here analyzed C(F170S) (a C protein mutant with the F170S mutation) with no STAT1-binding ability. C(F170S) lacked the ability to inhibit the IFN-alpha response, but retained the ability to inhibit the IFN-gamma response. IFN-gamma stimulation caused STAT1 phosphorylation, formation of the gamma-activated factor capable of binding to a gamma-activated sequence DNA probe, and STAT1 nuclear translocation, even in the presence of C(F170S). These results suggest that C protein has the STAT1-binding-independent anti-IFN-gamma mechanism, which targets processes after the STAT1 nuclear translocation event.

Gradient gel electrophoresis was used to examine the separation properties of novel cross-linking compounds for polyacrylamide (PAAm). At low %T and at the same %C protein migration difference is accentuated for bismethacrylamide cross-linked networks relative to bisacrylamide cross-linked networks. Similar properties were observed for cyclic monomers at low %T. This trend is maintained throughout the gradient. However, at higher %T migration differential relative to N,N'-methylenebisacrylamide (Bis) was less pronounced. Evidence from gradient gels suggests that reactivity and functionality of vinyl groups impose an overriding control over network formation.

Sendai virus (SeV) renders cells unresponsive to interferon (IFN)-alpha. To identify viral factors involved in this process, we examined whether recombinant SeVs, which could not express V protein, subsets of C proteins (C, C', Y1 and Y2) or any of four C proteins, retained the capability of impeding IFN-alpha-mediated responses. Among these viruses, only the 4C knockout virus completely lost the ability to suppress the induction of IFN-alpha-stimulated gene products and the subsequent establishment of an anti-viral state. These findings reveal crucial roles of the SeV C proteins in blocking IFN-alpha-mediated responses.

As a conserved non-coding RNA gene, transcripts of MALAT-1 localize predominately in the nucleus. However in G2/M cell cycle phase, MALAT-1 transcripts were surprisingly found to translocate from the nucleus into the cytoplasm. Investigation also found that in this process MALAT-1 interacts with an abundant nuclear factor, hnRNP C protein. Using a loss-of-function assay, we found that down-regulation of MALAT-1 expression compromised the cytoplasmic translocation of hnRNP C in the G2/M phase and resulted in G2/M arrest. In addition to characterize the physiological interaction between MALAT-1 and hnRNP C, our study also highlights the role of MALAT-1 in cell cycle regulation.

To investigate the role of adhesion molecules in C protein-induced myositis (CIM), a murine model of polymyositis (PM).CIM was induced in wild-type mice, L-selectin-deficient (L-selectin(-/-) ) mice, intercellular adhesion molecule 1 (ICAM-1)-deficient (ICAM-1(-/-) ) mice, and mice deficient in both L-selectin and ICAM-1 (L-selectin(-/-) ICAM-1(-/-) mice). Myositis severity, inflammatory cell infiltration, and messenger RNA expression in the inflamed muscles were analyzed. The effect of dendritic polyglycerol sulfate, a synthetic inhibitor that suppresses the function of L-selectin and endothelial P-selectin, was also examined.L-selectin(-/-) mice and L-selectin(-/-) ICAM-1(-/-) mice developed significantly less severe myositis compared to wild-type mice, while ICAM-1 deficiency did not inhibit the development of myositis. L-selectin(-/-) mice that received wild-type T cells developed myositis. Treatment with dendritic polyglycerol sulfate significantly diminished the severity of myositis in wild-type mice compared to treatment with control.These data indicate that L-selectin plays a major role in the development of CIM, whereas ICAM-1 plays a lesser role, if any, in the development of CIM. L-selectin-targeted therapy may be a candidate for the treatment of PM.

The binding of IgA with C-protein was studied and compared with that of jacalin. SDS- PAGE and Western blotting for various human IgA forms (IgA1, IgA2, serum IgA and secretory IgA) proved the specificity of C-protein binding and the superiority of biotinylated C-protein over biotinylated jacalin as probing immunochemical reagent for IgA detection. The obtained results proved the usefulness of employing C-protein / sepharose columns in isolation of IgA from the whole serum. Although, a linear quantitative relationship was established with pure IgA, the development of ELISA technique for quantification of IgA in whole serum was not possible in the present study. However, a proposed procedure was set for further work.

Extraction of regulatory proteins from thick and thin filaments of vertebrate striated muscle has proven to be an important approach in elucidating roles of these proteins in regulating contraction and in probing specific mechanisms of activation. For some proteins, such as LC2 and C protein, extraction has been fundamental in demonstrating the importance of these proteins in modulating contraction and the kinetics of cross-bridge interaction. For other proteins, such as TnC and troponin, extraction has provided significant insight into the importance of thin-filament intermolecular cooperativity in modulating Ca2+ sensitivity of the contractile process. A combination of extraction and readdition has provided a means of introducing mutated or derivatized proteins into fibers to accomplish a variety of experimental objectives. The use of this approach is likely to grow with the need to test the functional consequences of site-specific mutations as part of studies directed to mechanisms of regulation or altered regulation in heart and skeletal muscles under normal and pathophysiological conditions. Such studies are likely to include extraction in combination with other probes of function such as flash photolysis of reaction substrates or products within the cross-bridge interaction cycle. Although extraction is a powerful approach and is likely to be extended to proteins not discussed in this review, an essential element of experimental design in studies such as these is that appropriate control experiments be done to verify that observed effects of the extraction protocol are specifically attributable to the protein that is removed.

C-Proteins in developing, denervated, and dystrophic chicken skeletal muscles were examined by means of two-dimensional (2D) gel electrophoresis in combination with immunoblotting. In this analysis, the electrophoresis system which was devised by Hirabayashi (Anal. Biochem. 117, 443-451, 1981) provided excellent resolution; three C-protein variants, one fast-type (Cf) and two slow-types (CS3 and CS4) with different Mrs and pIs, were distinguished on a 2D gel. In the neonatal breast muscle, both Cf and CS3 were detected, but during postnatal development, CS3 disappeared from this muscle and Cf became only the C-protein isoform in the adult muscle. In posterior latissimus dorsi (PLD) muscle, both Cf and CS3 were similarly detected at the neonatal stage, but CS3 was replaced by CS4 as this muscle developed. When the breast and PLD muscles were denervated or suffered from muscular dystrophy, both CS3 and CS4 were co-expressed in these muscles in addition to Cf. These results definitely show that the C-protein isoform pattern varies during development and degeneration of chicken skeletal muscles, and in addition the dystrophic or denervated muscle differs from the neonatal muscle with regard to C-protein isoform expression. We suggest that chicken skeletal muscle degenerating due to denervation or muscular dystrophy does not simply recapture the nature of the neonatal muscle, but shifts in a somewhat different direction.

Avaliaram-se a composição bromatológica, as frações da proteína bruta (A, B1, B2, B3 e C) e dos carboidratos totais (A, B1, B2 e C) e as respectivas taxas de digestão das frações B1, B2 e B3 de proteínas e das frações A + B1 e B2 de carboidratos e do feno de capim-tifton 85, obtido de plantas colhidas com 28, 35, 42 e 56 dias de rebrota, adubadas com 75 kg/ha/corte de N. Os teores protéicos dos fenos com idades de rebrota de 28 a 56 dias variaram de 17,58 a 12,58%. Os valores das frações protéicas A, B1, B2, B3 e C apresentaram-se, respectivamente, entre 22,10 e 35,53%; 0,24 e 4,55%; 30,37 e 31,34%; 26,55 e 36,62%; e 5,75 e 6,76%, como proporções da proteína bruta total, nos fenos com idades de rebrota entre 28 e 56 dias. As taxas de digestão das frações protéicas B1, B2 e B3 encontraram-se entre 0,319 e 1,324; 0,0724 e 0,0936; e 0,0077 e 0,012 h -1, respectivamente, nos fenos com idades de rebrota entre 28 e 56 dias. Os teores de carboidratos totais variaram de 72,98 a 78,77%, em fenos com 28 a 56 dias de rebrota. Os valores das frações A, B1, B2 e C de carboidratos apresentaram-se entre 2,73 e 5,44%; 1,91 e 2,35%; 77,49 e 80,59%; e 13,59 e 17,87%, respectivamente, como proporções dos carboidratos totais, em fenos com idades entre 28 e 56 dias de rebrota. As taxas de digestão das frações de carboidratos A + B1 e B2 encontraram-se entre 0,181 e 0,20 e 0,04 e 0,0466 h -1, respectivamente, em fenos com idades entre 28 e 56 dias de rebrota. The chemical composition, crude protein fractions (A, B1, B2, B3 and C) and total carbohydrate fractions (A, B1, B2 and C), and respective degradation rate of B1, B2 and B3 protein fractions and A + B1 and B2 carbohydrate fractions of Tifton 85 bermudagrass hay from plants harvested with 28, 35, 42 and 56 days of regrowth, fertilized with 75 kg/ha/cut of N, were evaluated. The protein content of hays from 28 to 56 days of regrowth ranged from 17.58 to 12.58%. The values of A, B1, B2, B3 and C protein fractions presented between 22.1 and 35.53%; 0.24 and 4.55%; 30.37 and 31.34%; 26.55 and 36.62%, and, 5.75 and 6.76%, respectively, as a percentage of the total crude protein, in the hays with ages between 28 and 56 days of regrowth. The degradation rate of B1, B2 and B3 protein fractions presented between 0.319 and 1.324; 0.0724 and 0.0936, and, 0.0077 and 0.012 h -1, respectively, in the hays with ages between 28 and 56 days of regrowth. The total carbohydrates content ranged from 72.98 to 78.77%, for the hays with 28 to 56 days of age. The values of A, B1, B2 and C carbohydrate fractions presented between 2.73 and 5.44%; 1.91 and 2.35%; 77.49 and 80.59%, and, 13.59 and 17.87%, as a percentage of total carbohydrates, in hays with ages between 28 and 56 days of regrowth. The degradation rate of the A + B1 and B2 carbohydrate fractions presented between 0.181 and 0.20, and 0.04 and 0.0466 h -1, in hays with ages between 28 and 56 days of regrowth, respectively.

Electroporation was used as a powerful and simple method to probe to the intracellular distribution and trafficking of signal sequences. By coupling synthetic peptides to carrier reporter groups, specific amino acid sequences responsible for nucleolar targeting of Semliki Forest virus (SFV) Core (C) protein were found out. In the N-terminal part of the C protein the sequences 66KPKKKKTTKPKPKTQPKK83 92KKKDKQADKKKKP105 are able to situate BSA or KLH as reporter proteins in the nucleolus, suggesting that SFV C protein contains at least two independent nucleolar targeting sequences.

C-protein has previously been shown to bind to the light-meromyosin region of the myosin tail. Examination of mixtures of C-protein with heavy meromyosin or subfragment-2 or subfragment-1 in the analytical ultracentrifuge shows that there is also a binding site for C-protein in the subfragment-2 region of the tail.

Salmonella typhimurium was shown to contain a citrate-binding protein (C protein) which was purified to homogeneity from the periplasmic fraction released by cold osmotic shock. The protein is dimeric, has an apparent molecular weight of 28 000 and an isoelectric point of 6.1. Sodium ions were required for optimum substrate binding, however, the divalent cations Zn2+, Mg2+, and Co2+ were inhibitory. The C protein was relatively stable but sensitive to various detergents and chaotropic agents. Approximately one citrate molecule was bound per molecule of protein and citrate binding (Kd = 1–2.6 μM) was strongly competitively inhibited by DL-isocitrate and DL-fluorocitrate but not by other carboxylates. Neither succinate, glutamate, nor acetate were bound to the C protein. No apparent enzyme activity was associated with this protein. A concomitant reduction in the level of binding protein and in citrate transport activity occurred in osmotically shocked cells as well as with L-malate- or succinate-grown cells. Fluorocitrate-resistant mutants were simultaneously defective in citrate transport, citrate binding, and production of cross-reacting material. One transport-defective mutant did produce citrate binding protein.

The plasma decay of three groups of iodinated apoproteins on human very low density lipoproteins were evaluated in two normals, two subjects with endogenous hypertriglyceridemia and another two with dysbetalipoproteinemia. The apo beta decay was more rapid than that of the C apoproteins in all patients. The apo beta decay was more rapid for the normals than for either the subjects with hypertriglyceridemia or dysbetalipoprotenemia. The apo C protein had an irregular decay in the normals but decayed less irregularly for the hypertriglyceridemics. The arginine rich apoprotein had a decay somewhat similar to apo C protein in the normals. The apo beta protein of the α 2 very low density lipoprotein of a dysbetalipoproteinemic was consistent with a precursor relationship to the apo beta of beta very low density lipoprotein of this subject, but the arginine rich apoprotein was not.

Two experiments were conducted to study the protein and amino acid requirements of growing Large White female turkeys at temperatures of 7, 14, 21, and 28 C. In Experiment 1, five dietary treatment series (A, B, C, D and E) which ranged in protein content from 24.3 to 16.9, 20.4 to 14.2 and 17.8 to 11.9%, were fed during 8 to 11, 11 to 14, and 14 to 17 wk of age, respectively. The D diet series was also supplemented with methionine or lysine or both to equal the levels in the B series forming the D, DM, DL, and DML treatments. In Experiment 2, B and C protein levels were fed between 11 and 14 wk of age. Between 14 and 17 wk of age, the B, C, D, and E protein levels were fed to each group forming a 2 X 4 factorial arrangement. In Experiment 1, during 8 to 11 wk of age, body weight gain decreased when birds were fed diets containing less than 22.5% protein. From 11 to 14 wk of age, at 7 and 14 C, the C diet supported maximum gains but at 21 and 28 C, the B and A diets, respectively, resulted in heavier turkeys. With the D diet, methionine supplementation significantly (P less than .05) improved body weight of birds during 8 to 11 and 11 to 14 wk of age: lysine supplementation had no effect during 8 to 11 wk and inconsistent effects on gain during 11 to 14 and 14 to 17 wk of age. Results from 14 to 17 wk of age show that the protein requirement of female turkeys during this age was overestimated by the National Research Council in 1984.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorescence spectra of ANM-labeled, glycerinated rabbit psoas muscle fibers were recorded in relaxed, contracted, and rigor states. SDS polyacrylamide gel electrophoresis of the ANM-labeled muscle fibers indicated that proteins labeled with ANM were myosin heavy chain, C protein, and actin. In a relaxed state in the presence of ATP, myosin heavy chain was mainly labeled. During the transition from rigor to the relaxed or contracted state, there was a blue shift (about 5 nm) of the ANM emission spectrum. Similar experiments with FAM (N-(3-fluoranthyl)-maleimide)-labeled muscle fibers showed that these fluorescence changes were not artifacts due to the movement of muscle fibers. The fibers labeled in the ATP relaxing solution showed a marked decrease in both isometric force and unloaded shortening velocity (Vo), while in the fibers labeled in the rigor solution isometric tension was not markedly suppressed, though Vo decreased to the same extent as in the fibers labeled in the ATP relaxing solution. Fluorescence spectra of ANM-labeled HMM in different states were also measured. A fluorescence enhancement and a blue shift (about 5 nm) of the emission maximum were observed in HMM + MgATP or HMM + MgATP + F-actin in comparison with HMM + F-actin. These results suggest that the fluorescence spectra of the ANM-labeled muscle fibers reflect their conformational changes between the rigor state (in the absence of MgATP) and the relaxed or contracted state (in the presence of MgATP).

The Raman spectra of purified myosin, C-protein and myosin-C-protein complex in aqueous solution, as well as that of pelleted filaments, were analyzed. The analyses confirmed that C-protein adopts a predominantly non-alpha-helical structure, while myosin adopts a predominantly alpha-helical structure. Neither 10 mM MgCl2 nor filament formation induced large conformational changes of purified myosin. Thermal denaturation of purified myosin, however, induced large changes in the Raman spectrum owing to conformational changes. It is likely that the binding of myosin and C-protein is not accompanied by large conformational changes of the proteins.

Antibody labeling for C-protein observed in fluorescence microscopy shows that C-protein is located only in the middle one-third of each half of the A-band. In electron microscopy the labeling shows up as stripes spaced 430apart. The restricted location of C-protein to these stripes cannot be determined by electron microscopy alone. The earlier assumption that the stripes reflect the axial repeat of the myosin in the myosin filament ( Pepe, 1967 a ) is valid, since C-protein binds to the filaments with the repeat of the underlying molecules ( Pepe et al. , 1975 ; Rome et al. , 1973 ; Pepe, 1972 ). The labeling pattern for C-protein occurs in the same position as part of the labeling pattern for myosin. This explains why similar anti-myosin labeling patterns are observed in fluorescence microscopy regardless of the presence or absence of contaminating antibody to C-protein. In electron microscopy the labeling patterns are clearly different. This can be explained by the difference in detectability of antibody protein in fluorescence and electron microscopy. The antibody labeling experiments show that proteins other than C-protein are also present on the myosin filaments. Although antibody to these other proteins is detectable by antibody labeling, it is not detectable by immuno-diffusion against even the initial crude myosin extract.

Purified antibodies to the thick filament accessory proteins, C-protein, X-protein and H-protein, have been used to label fibres of three rabbit muscles, psoas (containing mainly fast white fibres), soleus (containing mainly slow red fibres) and plantaris (a muscle of mixed fibre type) and their location has been examined by electron microscopy. These accessory proteins are present on one or more of a set of eleven transverse stripes about 43 nm apart that have been observed previously in each half A-band. Each protein has a limited set of characteristic distributions. H-protein is present on stripe 3 (counting from the M-line) in the majority of psoas fibres but is absent in soleus and plantaris muscle. C-protein can occur (1) on stripes 4–11 (the commonest pattern seen in psoas); (2) on stripes 5–11 (in psoas and plantaris); (3) on stripe 3 together with stripes 5–11 (in plantaris); or (4) on none (in red fibres of all three muscles). X-protein can occur (1) on stripes 3–11 in the red fibres of all three muscles; (2) on stripe 4 only (in psoas and plantaris); (3) on stripes 3 and 4 (in psoas and plantaris) or (4) on none. Stripes labelled with anti-X are wider than those labelled with anti-C and consist of a doublet with an internal spacing of 16 nm. The patterns for the three accessory proteins, while overlapping, are in no case identical; this suggests the proteins do not simply substitute for one another. The precise axial positions of the anti-C labelled stripes differ from those of the anti-X stripes; the anti-X stripes lie about 8–9 nm further from the M-line than the corresponding anti-C stripes. This implies that the inner member of an X-protein doublet lies in a very similar position to a C-protein stripe. The anti-H labelled stripe seen in most psoas fibres lies 14 nm nearer the M-line than stripe 3 of the anti-X labelled array in psoas red fibres and is staggered from a continuation of the C-protein array by about 4 nm. The labelling patterns were constant within a fibre and suggest a very precise assembly mechanism. The number of classes of fibre, as defined by the accessory proteins present and their arrangement, exceeds the number of fibre types presently recognized.

There have been few in vivo studies of C apoprotein metabolism in man. Berman et al. (1) have carried out analyses of total C apoprotein kinetics following reinjection of radiolabelled VLDL. The simulated model resembled that for VLDL B apoprotein metabolism, comprising a series of 4 delipidation steps of the triglyceriderich particles during which C peptides become transferred to HDL, producing a final IDL particle which retains a small fraction of the original VLDL C apoprotein. The model did not identify the lipoprotein with which the C peptides entered the circulation, both VLDL and HDL fitting the data, but removal of C protein appeared to occur with HDL. The major aspects of this in vivo model coincided with findings observed consistently during the in vitro lipolysis of VLDL, and with studies of isolated cells and organs.

The detection of the gene ara C protein using a DNA-dependent in vitro protein synthesizing system represents the first isolation of an operon specific positive regulator with an in vivo role that has been genetically defined.