TELOMERIC LOCALIZATION OF TRF2, A NOVEL HUMAN TELOBOX PROTEIN

Natural chromosomal ends are stabilized by proteins that bind duplex t elomeric DNA repeats. In human cells, the TTAGGG Repeat factor 1 (TRF1 ) was identified by two independent studies, one screening for factors that bind duplex telomeric DNA(1,2) and the other screening for prote ins containing a particular Myb motif called the telobox, which is req uired for telomeric repeat recognition (Fig. 1a; refs 3-5). A second h uman open reading frame, orf2, contains a telobox sequence and encodes a polypeptide that specifically recognizes mammalian telomeric repeat DNA in vitro(3). We show that two proteins of 65 and 69 kD, expressed in HeLa cells, contain the orf2 telobox sequence. These proteins are collectively termed TRF2. Affinity-purified antibodies specific for an ti-TRF2 label the telomeres of intact human chromosomes, strengthening the correlation between occurrence of telobox and telomere-repeat rec ognition in vivo.