Ku is important for telomere maintenance, but not for differential expression of telomeric VSG genes, in African trypanosomes.
Trypanosome antigenic variation, involving differential expression of variant surface glycoprotein (VSG) genes, has a strong association with telomeres and with DNA recombination. All expressed VSGs are telomeric, and differential activation involves recombination into the telomeric environment or silencing/activation of subtelomeric promoters. A number of pathogen contingency gene systems associated with immune evasion involve telomeric loci, which has prompted speculation that chromosome ends provide conditions conducive for the operation of rapid gene switching mechanisms. Ku is a protein associated with eukaryotic telomeres that is directly involved in DNA recombination and in gene silencing. We have tested the hypothesis that Ku in trypanosomes is centrally involved in differential VSG expression. We show, via the generation of null mutants, that trypanosome Ku is closely involved in telomere length maintenance, more so for a transcriptionally active than an inactive telomere, but exhibits no detectable influence on DNA double strand break repair. The absence of Ku and the consequent great shortening of telomeres had no detectable influence either on the rate of VSG switching or on the silencing of the telomeric promoters of the VSG subset that is expressed in the tsetse fly.
Conway
Colin
C
Wellcome Centre for Molecular Parasitology, University of Glasgow, Anderson College, 56 Dumbarton Road, Glasgow, G11 6NU, Scotland, United Kingdom.
McCulloch
Richard
R
Ginger
Michael L
ML
Robinson
Nicholas P
NP
Browitt
Alison
A
Barry
J David
JD
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D034961:Antigens, Nuclear; D001665:Binding Sites; D015139:Blotting, Southern; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020868:Gene Silencing; D006720:Homozygote; D000072200:Ku Autoantigen; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D008969:Molecular Sequence Data; D009153:Mutagens; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010692:Phleomycins / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D012313:RNA / Q000378:metabolism; D011995:Recombination, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D016615:Telomere / Q000378:metabolism*; D014158:Transcription, Genetic; D014345:Trypanosoma; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000378:metabolism*
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009153:Mutagens; D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D010692:Phleomycins; D014643:Variant Surface Glycoproteins, Trypanosoma; D012313:RNA; D004247:DNA; D008741:Methyl Methanesulfonate; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen