Loss of cap structure causes mitotic defect in Tetrahymena thermophila telomerase mutants.
Mutation of the telomeric repeat sequence has severe cellular consequences in a variety of systems. A Tetrahymena thermophila telomerase template mutant, ter1-43AA, displays an acute mitotic chromosome segregation defect. In the study described here we investigated the molecular basis for this lethality. Although cloned ter1-43AA macronuclear telomeres had long tracts of wild-type G4T2 repeats, they were capped by a mixture of G4T3 repeats, shown previously to be non-lethal, and G4T4 repeats, the telomeric sequence normally found in hypotrichous ciliates such as Oxytricha. To test further the functionality of the G4T4 repeat sequence in T. thermophila, we devised a new template mutation, ter1-44+AA, that resulted in more uniform synthesis of this sequence at telomere caps in vivo. The ter1-44+AA mutant displayed the most severe mitotic defect reported to date, with up to 85% of the population having micronuclei in anaphase, providing firm evidence that the hypotrich repeat sequence is not functional in Tetrahymena. Surprisingly, in spite of the telomeric sequence mutation, neither the ter1-43AA nor ter1-44+AA mutant displayed any significant loss of telomere length regulation. These results demonstrate that loss of telomere cap integrity, rather than length regulation, leads to the anaphase defect.
Petcherskaia
Marina
M
Department of Biology, Lake Forest College, IL 60045, USA.
McGuire
Jennifer M
JM
Pherson
James M
JM
Kirk
Karen E
KE
D000705:Anaphase; D000818:Animals; D015139:Blotting, Southern; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D004275:DNA, Ribosomal / Q000737:chemistry; D008938:Mitosis; D008954:Models, Biological; D009154:Mutation; D010641:Phenotype; D019098:Telomerase / Q000235:genetics*; D016615:Telomere / Q000648:ultrastructure; D016808:Tetrahymena thermophila / Q000201:enzymology*
D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D019098:Telomerase