title: Neurospora importin α is required for normal heterochromatic formation and DNA methylation.
abstract: Heterochromatin and associated gene silencing processes play roles in development, genome defense, and chromosome function. In many species, constitutive heterochromatin is decorated with histone H3 tri-methylated at lysine 9 (H3K9me3) and cytosine methylation. In Neurospora crassa, a five-protein complex, DCDC, catalyzes H3K9 methylation, which then directs DNA methylation. Here, we identify and characterize a gene important for DCDC function, dim-3 (defective in methylation-3), which encodes the nuclear import chaperone NUP-6 (Importin α). The critical mutation in dim-3 results in a substitution in an ARM repeat of NUP-6 and causes a substantial loss of H3K9me3 and DNA methylation. Surprisingly, nuclear transport of all known proteins involved in histone and DNA methylation, as well as a canonical transport substrate, appear normal in dim-3 strains. Interactions between DCDC members also appear normal, but the nup-6(dim-3) allele causes the DCDC members DIM-5 and DIM-7 to mislocalize from heterochromatin and NUP-6dim-3 itself is mislocalized from the nuclear envelope, at least in conidia. GCN-5, a member of the SAGA histone acetyltransferase complex, also shows altered localization in dim-3, raising the possibility that NUP-6 is necessary to localize multiple chromatin complexes following nucleocytoplasmic transport.
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Andrew D
authors: AD
authors: Klocko
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Michael R
authors: MR
authors: Rountree
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Paula L
authors: PL
authors: Grisafi
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Shan M
authors: SM
authors: Hays
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Keyur K
authors: KK
authors: Adhvaryu
authors: Institute of Molecular Biology, University of Oregon, Eugene, Oregon, United States of America.
authors: Eric U
authors: EU
authors: Selker
mesh_terms: D003596:Cytosine / Q000378:metabolism; D019175:DNA Methylation / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics*; D020868:Gene Silencing; D006570:Heterochromatin / Q000235:genetics*; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics* / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics; D028901:alpha Karyopherins / Q000235:genetics* / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D006570:Heterochromatin; D006657:Histones; D028901:alpha Karyopherins; D003596:Cytosine; D011495:Histone-Lysine N-Methyltransferase; D008239:Lysine