Telomeric organization of a variable and inducible toxin gene family in the ancient eukaryote Giardia duodenalis.
Giardia duodenalis is the best-characterized example of the most ancient eukaryotes, which are primitively amitochondrial and anaerobic. The surface of Giardia is coated with cysteine-rich proteins. One family of these proteins, CRP136, varies among isolates and upon environmental stress. A repeat region within the CRP136 family is interchangeable by a cassette-like mechanism, generating further diversity in repeat size, copy number, and sequence. Flanking the 5' region of the CRP136 family is a novel protein kinase gene and an ankyrin homolog, creating a conserved unit. A short spacer separates the ankyrin gene from the variable, tandem array of rDNA gene units at a common breakpoint within the large subunit gene, which is followed by the (TAGGG)n telomeric sequence. Transcriptional up-regulation of the CRP136 family is accompanied by a switch in mRNA length and promoter, of de novo expression, and suggests that CRP136 mRNA induction is under the control of a telomerically regulated position effect, which evolved very early in the eukaryotic lineage.
Upcroft
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P
Queensland Institute of Medical Research, Bancroft Centre, Brisbane, Australia. peteru@qimr.edu.au
Chen
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N
Upcroft
J A
JA
D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping / Q000379:methods; D003001:Cloning, Molecular; D017125:Genes, Protozoan / Q000235:genetics*; D005872:Giardia / Q000235:genetics*; D008969:Molecular Sequence Data; D015800:Protozoan Proteins; D016615:Telomere / Q000235:genetics*
C097377:CRP136 protein, Giardia duodenalis; D015800:Protozoan Proteins