Overexpression of the enzyme, called tankyrase 1, is known to extend telomere length—it makes TRF1 fall off telomeres so that telomerase can gain access. So presumably too little tankyrase 1 will have the opposite effect, and simply shorten telomeres.
Or not. Dynek and Smith now find that cells lacking tankyrase 1 have a completely unexpected phenotype. They arrest in mitosis when their telomeres, though not covalently linked, nevertheless fail to separate. Tankyrase 1 is a poly(ADP-ribose) polymerase that dissociates TRF1 from telomeres based on the excess negative charge of all those ADP-ribose groups on TRF1. Whether it is TRF1 or another protein that is the relevant target for dissolving telomere pairing is unknown.
Telomere pairing is known to help chromosomes pair during meiosis, and may help damaged telomeres to repair each other by homologous recombination. It appears that the tankyrase mechanism is used especially for regulating telomere pairing, either instead of or in addition to the separase–cohesin system used on chromosome arms. Smith is now interested in how this pairing is regulated during the cell cycle. ▪