Progressive cis-inhibition of telomerase upon telomere elongation

In yeast, the constant length of telomeric DNA results from a negative regu lation of telomerase by the telomere itself. Here we follow the return to e quilibrium of an abnormally shortened telomere, We observe that telomere el ongation is restricted to a few base pairs per generation and that its rate decreases progressively with increasing telomere length, In contrast, in t he absence of telomerase or in the presence of an over-elongated telomere, the degradation rate linked to the succession of generations appears to be constant, i.e. independent of telomere length, Together, these results indi cate that telomerase is gradually inhibited at its site of action by the el ongating telomere. The implications of this finding for the dynamics of tel omere length regulation are discussed in this study.