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J Bag

Publications and source records attributed to J Bag.

45 records · Page 3Linked to original sources
PubMed1976

Studies on a nonpolysomal ribonucleoprotein coding for myosin heavy chains from chick embryonic muscles.

A messenger ribonucleoprotein (mRNP) particle containing the mRNA coding for the myosin heavy chain (MHC mRNA) has been isolated from the postpolysomal fraction of homogenates of 14-day-old chick embryonic muscles. The mRNP sediments in sucrose gradient as 120 S and has a characteristic buoyant density of 1.415 g/cm3, which corresponds to an RNA:protein ratio of 1:3.8. The RNA isolated from the 120 S particle behaved like authentic MHC mRNA purified from chick embryonic muscles with respect to electrophoretic mobility and ability to program the synthesis of myosin heavy chain in a rabbit reticulocyte lysate system as judged by multi-step co-purification of the in vitro products with chick embryonic leg muscle myosin added as carrier. The RNA obtained from the 120 S particle was as effective as purified MHC mRNA in stimulating the synthesis of the complete myosin heavy chains in rabbit reticulocyte lysate under conditions where non-muscle mRNAs had no such effect. Analysis of the protein moieties of the 120 S particle by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows the presence of seven distinct polypeptides with apparent molecular weights of 44,000, 49,000, 53,000, 81,000, 83,000, and 98,000, whereas typical ribosomal proteins are absent. These results indicate that the 120 S particles are distinct cellular entities unrelated to ribosomes or initiation complexes. The presence of muscle-specific mRNAs as cytoplasmic mRNPs suggests that these particles may be involved in translational control during myogenesis in embryonic muscles.

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PubMed1975

Cytoplasmic nonpolysomal messenger ribonucleoprotein containing actin messenger RNA in chicken embryonic muscles.

Cytoplasmic nonpolysomal mRNAs have been isolated in the form of 16-40S ribonucleoprotein particles from the postribosomal supernatant of 14-day-old chick embryonic muscles. An 8-20S RNA fraction isolated from these particles directs the synthesis of actin in a wheat germ embryo S-30 system, as judged by copurification of the products with chicken muscle actin by repeated cycles of G- to F-actin transformation; mobilities of the purified product on sodium dodecyl sulfate-polyacrylamide gels and urea gels; and analysis of the CNBr-cleaved peptides. The 16-40S particles have a buoyant density of 1.4 g/cm3 which corresponds to an RNA/protein ratio of 1:3. They do not contain detectable levels of ribosomal subunits, as judged by the absence of typical ribosomal proteins in the range of 15,000-30,000. They contain at least eight distinct polypeptide species in the molecular weight range of 44,000-100,000, including a prominent 44,000 species. The presence of these particles suggests that they may have a role in the regulation of translation in developing muscles.

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PubMedDate not supplied

Regulation of c-jun/AP-1 expression in rat L6 myoblasts.

Myogenic differentiation of skeletal myoblasts in culture is triggered by withdrawal of serum mitogens. Expression of one of the serum-inducible, immediate early genes, the protooncogene c-jun, is maintained under low-serum conditions during myogenic differentiation of L6 myoblasts. In this report we have used agents that modulate protein kinases and Ca2+ levels to investigate how the expression of c-jun and myogenin mRNA and also the activator protein 1 (AP-1) DNA-binding activity are regulated in differentiating L6 cells. Our results show that expression of c-jun and myogenin are regulated independent of each other. Furthermore, down regulation of c-jun expression does not cause an increase in myogenin expression, suggesting that c-jun does not suppress myogenin expression in these cells. Electrophoretic mobility shift and ultraviolet cross-linking analyses revealed that the AP-1 complexes of proliferating myoblasts and differentiating myotubes are formed of similar set of polypeptides, and the AP-1 binding activity is probably modulated by posttranslational modifications in differentiating L6 cells.

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PubMedDate not supplied

Expression of the protooncogene c-jun is maintained during myogenic differentiation in rat L6 myoblasts.

Skeletal myoblasts undergo terminal differentiation when maintained under low-mitogen conditions. We have examined the expression of c-jun, one of the growth-factor-inducible immediate-early genes, during myogenic differentiation of L6 myoblasts. The steady-state levels of c-jun mRNA, c-Jun polypeptide, and activator protein 1 binding activity were not markedly altered in L6 cells undergoing myogenic differentiation. Although expression of c-jun is induced by serum mitogens in fibroblasts and other cell lines, addition of high serum to proliferating myoblasts resulted in the activation of another immediate early gene junB, but not c-jun mRNA expression. These results indicate that regulation of c-jun may differ from that of other immediate early genes in L6 cells. Manipulation of myogenesis by exposing L6 cells to dimethyl sulfoxide also suggested that expression of myogenin and muscle differentiation could occur in the presence of high levels of c-Jun. Furthermore, expression of c-jun from Moloney murine leukaemia viral long-terminal repeat in transfected L6 cells confirmed that constitutive expression of c-jun does not interfere with myogenesis in L6 myoblasts. Therefore, regulation of c-jun expression in rat L6 cells differs from that in the mouse C2 cell line.

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