CHL1 is a nuclear protein with an essential ATP binding site that exhibits a size-dependent effect on chromosome segregation.
Saccharomyces cerevisiae chl1 mutants have a significant increase in the rate of chromosome missegregation. CHL1 encodes a 99 kDa predicted protein with an ATP binding site consensus, a putative helix-turn-helix DNA binding motif, and homology to helicases. Using site-directed mutagenesis, I show that mutations that are predicted to abolish ATP binding in CHL1 inactivate its function in chromosome segregation. Furthermore, overexpression of these mutations interferes with chromosome transmission of a 125 kb chromosome fragment in a wild-type strain. Polyclonal antibodies against CHL1 show that CHL1 is predominantly in the nuclear fraction of S. CEREVISIAE: CHL1 function is more critical for the segregation of small chromosomes. In chl1Delta1/chl1Delta1 mutants, artificial circular or linear chromosomes <150 kb in size exhibit near random segregation (0.12 per cell division), whereas all chromosomes tested >225 kb were lost at rates (5 x 10(-)(3) per cell division) comparable to that observed for endogenous chromosome III. These results reveal an important role for ATPases/DNA helicases in chromosome segregation. Such enzymes may alter DNA topology to allow loading of proteins involved in maintaining sister chromatid cohesion.
L Holloway
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Howard Hughes Medical Institute, Department of Genetics, University of Pennsylvania, 415 Curie Boulevard, Philadelphia, PA 19104, USA. hollowas@mail.med.upenn.edu
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015825:Chromosomes, Fungal / Q000235:genetics*; D016384:Consensus Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
C066751:CHL1 protein, S cerevisiae; D002868:Chromosomal Proteins, Non-Histone; D005656:Fungal Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases