An essential yeast gene encoding a TTAGGG repeat-binding protein.

Abstract

A yeast gene encoding a DNA-binding protein that recognizes the telomeric repeat sequence TTAGGG found in multicellular eukaryotes was identified by screening a Agtll expression library with a radiolabeled TTAGGG multimer. This gene, which we refer to as TBFI (TTAGGG repeat-binding factor 1), encodes a polypeptide with a predicted molecular mass of 63 kDa. The TBF1 protein, produced in vitro by transcription and translation of the cloned gene, binds to (TTAGGG) Among all eukaryotes examined to date, the telomere is a highly conserved structure designed to protect chromosomes from degradation and fusion (for reviews, see references 6 and 32). Telomeres are composed of multiple repeats of short sequence elements (typically 5 to 8 bp in length, with a GT-rich strand oriented 5' to 3' toward the end of the chromosome) and range in length from a few repeat units to >10 kb. The repeated sequence (TTAGGG)n is found at telomeres in all vertebrates, certain slime molds, and trypanosomes; (TTGGGG)n and (TlTITGGGG)n are found in the ciliated protozoan Tetrahymena and Oxytricha species, respectively; and (TG1_3)n is found in the yeast Saccharomyces cerevisiae. In organisms whose telomeres have been examined in detail, the GT strand extends 12 to 16 nucleotides (two repeats) beyond the complementary C-rich strand.Proteins (5,8,19). Biochemical (11, 31) and cytological (17) studies have shown that RAP1 is bound to these sites in vivo. Furthermore, mutations in RAP1 affect telomere length, clearly establishing a role for RAP1 in the regulation of telomere structure (11,22,29

The genome-wide expression response to telomerase deletion in Saccharomyces cerevisiae

“…The TDR included only a few genes previously implicated in telomere function. Three of these were down-regulated when telomeres were shortest: RAP1, a central negative regulator of telomere length (19); EBS1, a gene that contains an RRM RNA recognition motif and is also homologous to the telomerase component EST1 (20); and TBF1, which encodes a DNA-binding protein (21). Rap1p and its associated proteins regulate access of telomerase to the telomere in a lengthdependent manner (19); thus, RAP1 down-regulation could be an adaptive response to shortened telomeres.…”

PcMYB1, a novel plant protein containing a DNA‐binding domain with one MYB repeat, interacts in vivo with a light‐regulatory promoter unit

“…The N-terminal region of PcMYB1 exhibits a striking sequence similarity to the R1, R2 and R3 repeats of the animal MYB proteins as well as the R2 and R3 repeats et al, 1993), IBP1 (Lugert and Werr, 1994), TRF (Chong et al, 1995), TBF1 (Brigati et al, 1993), RAP1 (KOnig et al, 1996), XMYB1 (Bouwmeester et al, 1992), cMYB (Gonda eta/., 1985), C1 (Paz-Ares et al, 1987), GL-1 (Oppenheimer et al, 1991), MYB305 (Jackson eta/., 1991), and MYBST1 (Baranowskij et al, 1994). On the right, the percentage of sequence identity in the compared areas is given.…”

“…Two ORFs given in the dbEST database (designated AtMYB1-2 and OsMYB1; Figure 3) and four MYB-like DNAbinding proteins share this DNA-binding domain with PcMYBI: BPF1 from P. crispum binds MREPAL-p of the PcPAL 1 promoter (da Costa e Silva et al, 1993); IBP1 from Z. mays binds the initiator sequence of the Shrunken promoter and is thought to play a role in basal expression (Lugert and Werr, 1994); TRF recognizes the (TTAGGG) n sequence from Homo sapiens telomers and has been shown by elegant studies to be a component of human telomers (Chong et al, 1995); and TBF1 from Saccharomyces cerevisiae, which is essential for growth, binds in vitrotelomeric sequences of mammals and slime moulds (Bilaud et aL, 1996;Brigati et aL, 1993).…”

New telomeres in yeast are initiated with a highly selected subset of TG1-3 repeats.

“…This is similar to the results of in vitro studies of Tetrahymena telomerase (Harrington and Greider 1991), where new telomere sequences can be added at a distance from the T2G 4 repeats. In contrast, an organizing sequence does not appear to be needed to add new telomeres at chromosomal truncations in malaria (Scherf and Mattei 1992) and humans (Wilkie et al 1990;Morin 1991) and, in at least one developmental stage, Tetrahymena (Yu and Blackburn 19911. We imagine that certain proteins can bind to the organizer region [several possible candidate proteins have been identified (Liu and Tye 1991;Brigati et al 1993)] and stabilize the interaction of yeast telomerase with short G,T stretches upstream, allowing them to be used as an initial primer of a new telomere. Ill some cases, additional proteins that bind to the primer itself may play an important role.…”