DNA-binding modules of yeast Rap1 and related proteins
Yeast Rap1 DNA-binding activity is mediated by a pair of DNA-binding modules comprised of 2 3-helix bundles with an N-terminal arm, closely matching the structure of homeodomain and myb-type proteins. Human Rap1 has a single myb-like module, and may not bind DNA directly. Rap1, identified in budding yeast as repressor-activator protein 1, is a conserved telomere binding protein, also identified in fission yeast and mammals. In Saccharomyces cerevisiae, Rap1 directly binds DNA and is involved in transcriptional activation, gene silencing, as well as binding at numerous binding sites at each telomere, where it functions in telomere length regulation, telomeric position effect gene silencing and telomere end protection. Human Rap1 apparently does not bind telomeric DNA directly, but binds telomere repeat binding factor 2 (TRF2) via the Rap C-terminal domain (RCT). Rap1 may act by suppressing non-homologous end-joining. Yeast Rap1 has 2 myb-type DNA binding modules, a BRCT domain, and a RCT domain that recruits Sir3 and Sir4 proteins for gene silencing and Rif1 and Rif2 for telomere length maintenance. Human Rap1 has a similar domain architecture but has a single myb-like domain.
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