At some point in the extension process a sufficient number of regulatory factors that repress telomere extension become bound to the extending telomere. These factors include the TRF1 complexes, TRF2 complexes, telomerase, other factors, and the telomere itself. As repeats are added to the G-rich strand, and once lagging strand synthesis completes the duplex, new binding sites become available for these repressive factors. Once a balance is reached between telomere extension and the telomere repression factors, extension ceases. In this state extension machinery disassociates, leaving the telomere to be folded into a stable conformation.
This module details a single transit through the telomere extension process, detailing the addition of two repeats, and the corresponding synthesis of a section of lagging strand. An actual round of in vivo telomere extension would require thousands of telomere repeat additions, and it is the repressive effect of the factors bound to these repeats that turns off telomere extension (Moldovan et al. 2007).