Annexin II is associated with mRNAs which may constitute a distinct subpopulation.
Protein-mRNA interactions affect mRNA transport, anchorage, stability and translatability in the cytoplasm. During the purification of three subpopulations of polysomes, it was observed that a 36-kDa protein, identified as annexin II, is associated with only one specific population of polysomes, namely cytoskeleton-associated polysomes. This association appears to be calcium-dependent since it was sensitive to EGTA and could be reconstituted in vitro. UV irradiation resulted in partial, EGTA-resistant cross-linking of annexin II to the polysomes. Binding of (32)P-labelled total RNA to proteins isolated from the cytoskeleton-bound polysomes on a NorthWestern blot resulted in a radioactive band having the same mobility as annexin II and, most importantly, purified native annexin II immobilized on nitrocellulose specifically binds mRNA. The mRNA population isolated from cytoskeleton-bound polysomes binds to annexin II with the highest affinity as compared with those isolated from free or membrane-bound polysomes. Interestingly, the annexin II complex, isolated from porcine small intestinal microvilli was a far better substrate for mRNA binding than the complex derived from transformed Krebs II ascites cells. When cytoskeleton-associated polysomes were split into 60 S and 40 S ribosomal subunits, and a peak containing mRNA complexes, annexin II fractionated with the mRNAs. Finally, using affinity purification of mRNA on poly(A)(+)-coupled magnetic beads, annexin II was only detected in association with messenger ribonucleoproteins (mRNPs) present in the cytoskeletal fraction (non-polysomal mRNPs). These results, derived from both in vitro experiments and cell fractionation, suggest that annexin II binds directly to the RNA moiety of mRNP complexes containing a specific population of mRNAs.
Vedeler
A
A
Department of Biochemistry and Molecular Biology, University of Bergen, Arstadveien 19, N-5009 Bergen, Norway. Anni.Vedeler@pki.uib.no
Hollås
H
H
D000818:Animals; D017306:Annexin A2 / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D005615:Freezing; D051379:Mice; D011132:Polyribosomes / Q000378:metabolism; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D017306:Annexin A2; D012333:RNA, Messenger; D016601:RNA-Binding Proteins