Isolation and characterization of two Saccharomyces cerevisiae genes that encode proteins that bind to (TG1-3)n single strand telomeric DNA in vitro.

By screening lambda gt11 libraries with a radiolabeled (TG1-3)n oligonucleotide, two Saccharomyces cerevisiae genes were identified that encode polypeptides that recognize the single-stranded telomeric repeat sequence (TG1-3)n. The first gene, NSR1, a previously identified gene, encodes a protein involved in ribosomal RNA maturation and possibly in transport of proteins into the nucleus. The second gene, GBP2 (G-strand Binding Protein), is an anonymous open reading frame from chromosome III. These two genes contain RNA recognition motifs (RRMs) that are found in proteins that interact with RNA. Both Nsr1p and Gbp2p bind specifically to yeast single strand (TG1-3)n DNA in vitro. To test whether these two proteins associate with telomeres in vivo, strains were constructed in which one or both of these genes were either disrupted or overexpressed. None of these alterations affected telomere length or telomere position effect. The potential role of these two (TG1-3)n binding proteins is discussed.