title: A WD40-repeat containing protein, similar to a fungal co-repressor, is required for transcriptional gene silencing in Chlamydomonas.
abstract: In higher plants, mammals, and filamentous fungi, transcriptional gene silencing is frequently associated with DNA methylation. However, recent evidence suggests that certain transgenes can be inactivated by a methylation independent mechanism. In the unicellular green alga Chlamydomonas reinhardtii, single-copy transgenes are transcriptionally silenced without discernible cytosine methylation of the introduced DNA. We have isolated a Chlamydomonas gene, Mut11, which is required for the transcriptional repression of single-copy transgenes. Mut11 appears to have a global role in gene regulation since it also affects transposon mobilization, cellular growth, and sensitivity to DNA damaging agents. In transient expression assays, a fusion protein between the predicted Mut11 gene product (Mut11p) and E. coli beta-glucuronidase localizes predominantly to the nucleus. Mut11p, a polypeptide of 370 amino acids containing seven WD40 repeats, is highly homologous to proteins of unknown function that are widely distributed among eukaryotes. Mut11p also shows similarity to the C-terminal domain of TUP1, a global transcriptional co-repressor in fungi. Based on these findings we speculate that, in Chlamydomonas, the silencing of certain single-copy transgenes and dispersed transposons integrated into euchromatic regions may occur by a mechanism(s) similar to those involving global transcriptional repressors. Our results also support the existence, in methylation-competent organisms, of a mechanism(s) of transcriptional (trans)gene silencing that is independent of DNA methylation.
authors.affiliation: School of Biological Sciences and Plant Science Initiative, University of Nebraska - Lincoln, E211 Beadle Center, Post Office Box 880666, Lincoln, NE 68588-0666, USA.
authors.forename: Chaomei
authors.initials: C
authors.lastname: Zhang
authors.forename: Dancia
authors.initials: D
authors.lastname: Wu-Scharf
authors.forename: Byeong-ryool
authors.initials: BR
authors.lastname: Jeong
authors.forename: Heriberto
authors.initials: H
authors.lastname: Cerutti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D020868:Gene Silencing; D017343:Genes, Plant; D017125:Genes, Protozoan; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid
chemical_list: D010940:Plant Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins