.....Previously we demonstrated that in Tetrahymena, the telomeric 3' overhang is protected by a three protein complex composed of Pot1a, Tpt1 and Pat1. Here we show that that Tpt1 and Pat1 associate with a fourth protein, Pat2 (Pot1 associated in Tetrahymena 2). Mass spectrometry of proteins co-purifying with Pat1 or Tpt1 identified peptides from Pat2, Pot1a, Tpt1 and Pat1. The lack of other proteins co-purifying with Pat1 or Tpt1 implies that the overhang is protected by a four protein Pot1a-Tpt1-Pat1-Pat2 complex. We verified that Pat2 localizes to telomeres but we were unable to detect direct binding to telomeric DNA. Cells depleted of Pat2 continue to divide but the telomeres exhibit gradual shortening. The lack of growth arrest indicates that, in contrast to Pot1a and Tpt1, Pat2 is not required to sequester the telomere from the DNA repair machinery. Instead, Pat2 is needed to regulate telomere length most likely by acting in conjunction with Pat1 to allow telomerase access to the telomere.