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J. Cell Biol.,
Volume 140, Number 6, March 23, 1998 1463-1473
Developmental, The protein 4.1 superfamily is comprised of a
diverse group of cytoplasmic proteins, many of which
have been shown to associate with the plasma membrane via binding to specific transmembrane proteins.
Coracle, a Drosophila protein 4.1 homologue, is required during embryogenesis and is localized to the cytoplasmic face of the septate junction in epithelial cells.
Using in vitro mutagenesis, we demonstrate that the
amino-terminal 383 amino acids of Coracle define a
functional domain that is both necessary and sufficient for proper septate junction localization in transgenic
embryos. Genetic mutations within this domain disrupt
the subcellular localization of Coracle and severely affect its genetic function, indicating that correct subcellular localization is essential for Coracle function.
Furthermore, the localization of Coracle and the transmembrane protein Neurexin to the septate junction display an interdependent relationship, suggesting that
Coracle and Neurexin interact with one another at the
cytoplasmic face of the septate junction. Consistent with
this notion, immunoprecipitation and in vitro binding
studies demonstrate that the amino-terminal 383 amino
acids of Coracle and cytoplasmic domain of Neurexin
interact directly. Together these results indicate that
Coracle provides essential membrane-organizing functions at the septate junction, and that these functions
are carried out by an amino-terminal domain that is
conserved in all protein 4.1 superfamily members.
Program in Cell and
Molecular Biology, Duke University, Durham, North Carolina 27708-1000
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