Proteins from rat liver cytosol which stimulate mRNA transport. Purification and interactions with the nuclear envelope mRNA translocation system.
Two polysome-associated proteins with particular affinities for poly(A) have been purified from rat liver. These proteins stimulate the efflux of mRNA from isolated nuclei in conditions under which such efflux closely stimulates mRNA transport in vivo, and they are therefore considered as mRNA-transport-stimulatory proteins. Their interaction with the mRNA-translocation system in isolated nuclear envelopes has been studied. The results are generally consistent with the most recently proposed kinetic model of mRNA translocation. One protein, P58, has not been described previously. It inhibits the protein kinase that down-regulates the NTPase, it enhances the NTPase activity in both the presence and the absence of poly(A) and it seems to increase poly(A) binding in unphosphorylated, but not in phosphorylated, envelopes. The other protein, P31, which probably corresponds to the 35,000-Mr factor described by Webb and his colleagues, enhances the binding of poly(A) to the mRNA-binding site in the envelope, thus stimulating the phosphoprotein phosphatase and, in consequence, the NTPase. The possible physiological significance of these two proteins is discussed.
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000302:isolation & purification* / Q000502:physiology; D003600:Cytosol / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D009685:Nuclear Envelope / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D043583:Nucleoside-Triphosphatase; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D011061:Poly A / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins; D051381:Rats; D011919:Rats, Inbred Strains
D002352:Carrier Proteins; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011061:Poly A; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D010744:Phosphoric Monoester Hydrolases; D043583:Nucleoside-Triphosphatase