The mRNA-binding Protein YB-1 (p50) Prevents Association of the Eukaryotic Initiation Factor eIF4G with mRNA and Inhibits Protein Synthesis at the Initiation Stage

• Published in: The Journal of biological chemistry Vol. 278; no. 16; pp. 13936 - 13943
• Main Authors: Nekrasov, Maxim P., Ivshina, Maria P., Chernov, Konstantin G., Kovrigina, Elizaveta A., Evdokimova, Valentina M., Thomas, Adri A.M., Hershey, John W.B., Ovchinnikov, Lev P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 18.04.2003; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Blotting, Northern; Blotting, Western; CCAAT-Enhancer-Binding Proteins - isolation & purification; CCAAT-Enhancer-Binding Proteins - metabolism; CCAAT-Enhancer-Binding Proteins - physiology; Cell-Free System; Centrifugation, Density Gradient; Cytoplasm - metabolism; DNA-Binding Proteins; Dose-Response Relationship, Drug; Eukaryotic Initiation Factor-4G - metabolism; Models, Biological; NFI Transcription Factors; Nuclear Proteins; Protein Binding; Protein Biosynthesis; Protein Structure, Tertiary; Rabbits; Reticulocytes - metabolism; Ribosomes - metabolism; RNA - metabolism; RNA, Messenger - metabolism; Sucrose - pharmacology; Time Factors; Transcription Factors; Y-Box-Binding Protein 1
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M209145200

The cytoplasmic messenger ribonucleoprotein particles of mammalian somatic cells contain the protein YB-1, also called p50, as a major core component. YB-1 is multifunctional and involved in regulation of mRNA transcription and translation. Our previous studies demonstrated that YB-1 stimulates initiation of translation in vitro at a low YB-1/mRNA ratio, whereas an increase of YB-1 bound to mRNA resulted in inhibition of protein synthesis in vitro and in vivo. Here we show that YB-1-mediated translation inhibition in a rabbit reticulocyte cell-free system is followed by a decay of polysomes, which is not a result of mRNA degradation or its functional inactivation. The inhibition does not change the ribosome transit time, and therefore, it affects neither elongation nor termination of polypeptide chains and only occurs at the stage of initiation. YB-1 induces accumulation of mRNA in the form of free messenger ribonucleoprotein particles,i.e. it blocks mRNA association with the small ribosomal subunit. The accumulation is accompanied by eukaryotic initiation factor eIF4G dissociation from mRNA. The C-terminal domain of YB-1 is responsible for inhibition of translation as well as the disruption of mRNA interaction with eIF4G.