title: Real-time visualization of ZBP1 association with beta-actin mRNA during transcription and localization.
abstract: BACKGROUND
  mRNA localization in somatic cells is an important mechanism for gene expression regulation. In fibroblasts, the protein ZBP1 associates with the sequence that localizes beta-actin mRNA to the leading edge of fibroblasts, augmenting motility. beta-actin mRNA localizes in a cytoskeleton-dependent manner, depending on intact actin and myosin ATP-hydrolysis, and is largely bound to the actin cytoskeleton. The ZBP1 protein contains four KH RNA binding domains and a classic RBD RNA binding domain. It also contains a putative nuclear import and export sequence, suggesting a nuclear phase in this protein's function.
  
  
  RESULTS
  Using high-speed imaging, we show here the targeting of this RNA binding protein to beta-actin pre-mRNA transcripts in the nuclei of living cells and measure the residence time of the RNA-protein complex before it leaves the transcription site. Then, the RNA-protein particle is exported to the cytoplasm, where it localizes at velocities of 0.6 microm/s by using actin filaments and/or microtubules. This RNA-ZBP1 complex is required for cytoplasmic localization in fibroblasts; mislocalizing the protein also mislocalizes the RNA, and expressing the protein in a ZBP1-deficient cell line induces beta-actin mRNA localization.
  
  
  CONCLUSIONS
  This work demonstrates that the RNA-protein association, essential for cytoplasmic localization, begins as soon as the RNA is transcribed. The ZBP1 then forms a ribonucleoprotein particle and moves in a myosin-dependent fashion by using the cytoskeleton for directional transport.
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Oleynikov
authors.forename: Robert H
authors.initials: RH
authors.lastname: Singer
mesh_terms: D000199:Actins / Q000235:genetics* / Q000378:metabolism; D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D030161:Avian Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002642:Chick Embryo; D003593:Cytoplasm / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D000199:Actins; D000903:Antibiotics, Antineoplastic; D030161:Avian Proteins; D005231:Fatty Acids, Unsaturated; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; C498636:ZBP1 protein, Gallus gallus; D009218:Myosins; C038753:leptomycin B