title: Structure and expression of the maize (Zea mays L.) SUN-domain protein gene family: evidence for the existence of two divergent classes of SUN proteins in plants.
abstract: BACKGROUND
  The nuclear envelope that separates the contents of the nucleus from the cytoplasm provides a surface for chromatin attachment and organization of the cortical nucleoplasm. Proteins associated with it have been well characterized in many eukaryotes but not in plants. SUN (Sad1p/Unc-84) domain proteins reside in the inner nuclear membrane and function with other proteins to form a physical link between the nucleoskeleton and the cytoskeleton. These bridges transfer forces across the nuclear envelope and are increasingly recognized to play roles in nuclear positioning, nuclear migration, cell cycle-dependent breakdown and reformation of the nuclear envelope, telomere-led nuclear reorganization during meiosis, and karyogamy.
  
  
  RESULTS
  We found and characterized a family of maize SUN-domain proteins, starting with a screen of maize genomic sequence data. We characterized five different maize ZmSUN genes (ZmSUN1-5), which fell into two classes (probably of ancient origin, as they are also found in other monocots, eudicots, and even mosses). The first (ZmSUN1, 2), here designated canonical C-terminal SUN-domain (CCSD), includes structural homologs of the animal and fungal SUN-domain protein genes. The second (ZmSUN3, 4, 5), here designated plant-prevalent mid-SUN 3 transmembrane (PM3), includes a novel but conserved structural variant SUN-domain protein gene class. Mircroarray-based expression analyses revealed an intriguing pollen-preferred expression for ZmSUN5 mRNA but low-level expression (50-200 parts per ten million) in multiple tissues for all the others. Cloning and characterization of a full-length cDNA for a PM3-type maize gene, ZmSUN4, is described. Peptide antibodies to ZmSUN3, 4 were used in western-blot and cell-staining assays to show that they are expressed and show concentrated staining at the nuclear periphery.
  
  
  CONCLUSIONS
  The maize genome encodes and expresses at least five different SUN-domain proteins, of which the PM3 subfamily may represent a novel class of proteins with possible new and intriguing roles within the plant nuclear envelope. Expression levels for ZmSUN1-4 are consistent with basic cellular functions, whereas ZmSUN5 expression levels indicate a role in pollen. Models for possible topological arrangements of the CCSD-type and PM3-type SUN-domain proteins are presented.
authors.affiliation: Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL 32306-4370, USA.
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Murphy
authors.forename: Carl R
authors.initials: CR
authors.lastname: Simmons
authors.forename: Hank W
authors.initials: HW
authors.lastname: Bass
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D020033:Protein Isoforms