THE STRUCTURE OF THE YEAST TELOMERIC PROTEIN RAP1 IN COMPLEX WITH DNA: HOW TELOMERIC DNA SEQUENCES ARE RECOGNISED. D. Rhodes, P. Konig, R. Giraldo and L. Chapman, MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK

Telomeres are the specialised nucleoprotein complexes that form the termini of eukaryotic chromosomes. These structures are essential for chromosome stability, are sites of transcriptional silencing and are required for the association and organisation of chromosomes within the nucleus.

In the yeast S. Cerevisiae the telomeric DNA is packaged by the non-histone protein RAP1 (1). RAP1 is a particularly interesting protein since it can bind both double stranded DNA and DNA-quadruplexes (2). In order to understand how RAP1 binds to the unusual sequences of telomeric DNA we have solved the crystal structure of the DNA-binding domain of RAP1 bound to an 18bp telomeric DNA fragment at 2.25 Å resolution. The protein contains two similar domains that bind DNA in a tandem orientation, recognising a tandemly repeated DNA sequence. The domains are structurally related to the homeodomain and Myb motif, but show novel features in their DNA-binding mode. This structure provides the first insight into the recognition of the conserved telomeric DNA sequences by a protein (3).

1. Shore, D. (1994) Trends Genet. 10:408

2. Giraldo, R. and Rhodes, D. (1994) EMBO J. 13:2411

3. Konig, P., Giraldo, R., Chapman, L. and Rhodes, D. (1996) Cell, April 1996.