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Mol. Cell. Biol., Apr 1997, 2158-2165, Vol 17, No. 4
AF Ross, Y Oleynikov, EH Kislauskis, KL Taneja and RH Singer
Localization of beta-actin mRNA to the leading edge of fibroblasts requires
the presence of conserved elements in the 3' untranslated region of the
mRNA, including a 54-nucleotide element which has been termed the "zipcode"
(E. Kislauskis, X. Zhu, and R. H. Singer, J. Cell Biol. 127:441-451, 1994).
In order to identify proteins which bind to the zipcode and possibly play a
role in localization, we performed band- shift mobility assays, UV
cross-linking, and affinity purification experiments. A protein of 68 kDa
was identified which binds to the proximal (to the coding region) half of
the zipcode with high specificity (ZBP-1). Microsequencing provided unique
peptide sequences of approximately 15 residues each. Degenerate primers
corresponding to the codons derived from the peptides were synthesized and
used for PCR amplification. Screening of a chicken cDNA library resulted in
isolation of several clones providing a DNA sequence encoding a 67.7- kDa
protein with regions homologous to several RNA-binding proteins, such as
hnRNP E1 and E2, and with consensus mRNA recognition motif with RNP1 and 2
motifs and a putative REV-like nuclear export signal. Antipeptide
antibodies were raised in rabbits which bound to ZBP-1 and
coimmunoprecipitated proteins of 120 and 25 kDa. The 120-kDa protein was
also obtained by affinity purification with the RNA zipcode sequence, along
with a 53-kDa protein, but the 25-kDa protein appeared only in
immunoprecipitations. Mutation of one of the conserved sequences within the
zipcode, an ACACCC element in its proximal half, greatly reduced its
protein binding and localization properties. These data suggest that the
68-kDa ZBP-1 we have isolated and cloned is an RNA-binding protein that
functions within a complex to localize beta- actin mRNA.
Copyright © 1997, American Society for Microbiology
Characterization of a beta-actin mRNA zipcode-binding protein
Department of Cell Biology, University of Massachusetts Medical School, Worcester 01655, USA.
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