Two novel proteins, dos1 and dos2, interact with rik1 to regulate heterochromatic RNA interference and histone modification.
BACKGROUND
Chromosomal behavior during mitosis and meiosis depends in part on heterochromatic modifications such as histone H3 lysine-9 methylation (H3K9me). In fission yeast, the Heterochromatin Protein 1 homolog Swi6 recognizes H3K9me, silences transcription, and retains cohesin at pericentromeric repeats. Heterochromatin formation also depends on processing of transcripts derived from centromeric repeats by the RNAi machinery. The DDB1 homolog, Rik1, and histone methyltransferase, Clr4, act in a complex to promote H3K9me. However, the mechanism underlying this interaction is poorly understood.


RESULTS
Using a cytological screen, we have identified two novel genes, dos1(+) and dos2(+), which are required for localization of Swi6. Deletion of either of these genes results in mitotic and meiotic chromosome missegregation, defects in mitotic centromeric cohesion and meiotic telomere clustering, and loss of heterochromatic silencing. Dos1 is predominantly located in the nucleus in a Dos2-dependent manner and directly interacts with Rik1. Each of these genes is required for the association of H3K9me with centromeric repeats, as well as for the production of small interfering RNAs.


CONCLUSIONS
Dos1 and Dos2 are required for the formation of heterochromatin in fission yeast. We hypothesize that the physical interaction between Dos1 and Rik1 represents a role in regulating activity of the Rik1/Clr4 complex. Dos2 contributes to this role by regulating Dos1 localization. Our findings suggest a mechanism for recruitment of Clr4 in the RNAi-dependent heterochromatin pathway, in which Dos1 and Dos2 are essential.
Li
Fei
F
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.
Goto
Derek B
DB
Zaratiegui
Mikel
M
Tang
Xie
X
Martienssen
Rob
R
Cande
W Zacheus
WZ
D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D017931:DNA Primers; D049452:Green Fluorescent Proteins; D006570:Heterochromatin / Q000378:metabolism*; D011495:Histone-Lysine N-Methyltransferase; D006657:Histones / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D008856:Microscopy, Fluorescence; D021381:Protein Transport / Q000502:physiology; D034622:RNA Interference / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012568:Schizosaccharomyces; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D017931:DNA Primers; D006570:Heterochromatin; D006657:Histones; C489651:Rik1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; C465958:Swi6 protein, S pombe; D049452:Green Fluorescent Proteins; D008780:Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; C112744:clr4 protein, S pombe