Slx1-Slx4 are subunits of a structure-specific endonuclease that maintains ribosomal DNA in fission yeast

• Published in: Molecular biology of the cell 2004-01, Vol.15 (1), p.71-80
• Main Authors: Coulon, Stéphane, Gaillard, Pierre-Henri L, Chahwan, Charly, McDonald, William Hayes, Yates, 3rd, John R, Russell, Paul
• Format: Article
• Language: English
• Subjects: Chromatin - metabolism; DNA, Ribosomal; DNA-Binding Proteins - metabolism; Endonucleases - metabolism; Microscopy, Fluorescence; Models, Molecular; Molecular Sequence Data; Protein Subunits - metabolism; Recombination, Genetic; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - genetics; Schizosaccharomyces - genetics; Schizosaccharomyces - metabolism; Schizosaccharomyces pombe; Schizosaccharomyces pombe Proteins - metabolism; Sequence Alignment
• ISSN: 1059-1524; 1939-4586; 1059-1524
• DOI: 10.1091/mbc.E03-08-0586

In most eukaryotes, genes encoding ribosomal RNAs (rDNA) are clustered in long tandem head-to-tail repeats. Studies of Saccharomyces cerevisiae have indicated that rDNA copy number is maintained through recombination events associated with site-specific blockage of replication forks (RFs). Here, we describe two Schizosaccharomyces pombe proteins, homologs of S. cerevisiae Slx1 and Slx4, as subunits of a novel type of endonuclease that maintains rDNA copy number. The Slx1-Slx4-dependent endonuclease introduces single-strand cuts in duplex DNA on the 3' side of junctions with single-strand DNA. Deletion of Slx1 or Rqh1 RecQ-like DNA helicase provokes rDNA contraction, whereas simultaneous elimination of Slx1-Slx4 endonuclease and Rqh1 is lethal. Slx1 associates with chromatin at two foci characteristic of the two rDNA repeat loci in S. pombe. We propose a model in which the Slx1-Slx4 complex is involved in the control of the expansion and contraction of the rDNA loci by initiating recombination events at stalled RFs.