SR proteins preferentially associate with mRNAs in the nucleus and facilitate their export to the cytoplasm.
Different classes of RNA are exported to the cytoplasm by distinct mechanisms. Each class of RNA forms distinct complexes with nuclear proteins prior to its export to the cytoplasm. In our attempt to obtain comprehensive information of protein factors that specifically associate with mRNAs in the nucleus, we performed in vivo UV-crosslinking analysis after microinjection of various RNAs into Xenopus oocyte nucleus. We found a group of proteins preferentially crosslinked to mRNAs. Immunoprecipitation experiments revealed that some of the crosslinked signals corresponded to SR (serine/arginine-rich) proteins, a family of essential RNA-binding proteins involved in pre-mRNA splicing. It was previously suggested that some members of SR protein family are involved in export of a specific intronless mRNA, histone H2A mRNA and some spliced mRNAs. However, it is still to be clarified if SR proteins are involved in export of general mRNAs, especially general intronless mRNAs that do not contain specific RNA export elements. When we microinjected an antibody against SR proteins into the nucleus, export of mRNAs was severely inhibited, regardless of whether the mRNAs were produced via pre-mRNA splicing or not, whereas export of other RNAs was not affected. These results unequivocally showed that SR proteins are involved in export of both general intronless and spliced mRNAs.
Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, and CREST, JST (Japan Science and Technology Agency), Kawaguchi, Saitama 332-0012, Japan.
Kaoru
K
Masuyama
Ichiro
I
Taniguchi
Naoyuki
N
Kataoka
Mutsuhito
M
Ohno
D000818:Animals; D000906:Antibodies / Q000276:immunology; D002467:Cell Nucleus / Q000276:immunology / Q000378:metabolism* / Q000528:radiation effects; D003593:Cytoplasm / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism / Q000528:radiation effects; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000276:immunology / Q000378:metabolism*; D014466:Ultraviolet Rays; D014981:Xenopus
D000906:Antibodies; D012333:RNA, Messenger; D016601:RNA-Binding Proteins