title: Cell-free synthesis of a larger-molecular-weight precursor of cytochrome c oxidase subunit V from rat liver and the distribution of its mRNA between free and membrane-bound polysomes.
abstract: Poly(A)-rich RNA from phenol-extracted rat liver polysomes was translated in a heterologous cell-free system derived from wheat germs. The labeled translation products were incubated with an antiserum against cytochrome c oxidase subunit V. After immunoprecipitation and affinity chromatography with protein-A-Sepharose, the isolated antigen-immunoglobulin complexes were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and fluorography. Only one protein with an apparent molecular weight of 15 500 was visualized. In immunocompetition experiments with unlabeled individual cytochrome c oxidase subunits IV, V, VI or VII only subunit V could compete with the 15 500-Mr protein synthesized in vitro. Two-dimensional fingerprints of cytochrome c oxidase subunit V and the polypeptide synthesized in vitro showed a high degree of similarity. It is concluded that the cytochrome c oxidase subunit V is synthesized as a precursor with an amino-terminal extension of about 25 amino acids. It was possible to convert the precursor of cytochrome c oxidase subunit V synthesized in vitro to its mature form by intact mitochondria as well as by submitochondrial particles. A chain length of 830 +/- 70 nucleotides was estimated for the poly(A)-rich mRNA of the higher-molecular-weight precursor of rat liver cytochrome c oxidase subunit V. Assuming a molecular weight of 15 500 for the precursor a non-coding region of about 300 nucleotides must exist. In experiments on the site of synthesis it is shown that the poly(A)-rich RNA for the higher-molecular-weight precursor of cytochrome c oxidase subunit V is found in free, loosely and tightly membrane-bound polyribosomes.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D003576:Electron Transport Complex IV / Q000096:biosynthesis* / Q000235:genetics; D004792:Enzyme Precursors / Q000096:biosynthesis* / Q000235:genetics; D007120:Immunochemistry; D008099:Liver / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D011132:Polyribosomes / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats
chemical_list: D004792:Enzyme Precursors; D012333:RNA, Messenger; D003576:Electron Transport Complex IV