RAP1 (Repressor Activator Protein) is a multifunctional genetic regulator in yeast (S. cerevisiae). It is a transcription activator of some genes involved in producing ribosomal proteins, as well as acting as a transcription repressor of HMR and HML. The model above depicts another function of RAP1, transcriptional silencing of telomeric DNA by forming heterochromatin. RAP1 does this by binding to double-stranded telomeric DNA and recruiting its co-factors SIR(3/4) and RIF1. RAP1 is abundant around telomeric DNA, located at the ends of chromosomes, with one molecule found roughly every 18bp of telomeric DNA!
RAP1 has 2 predominant domains which share a great deal of symmetry but have some minor differences. Domains 1 and 2 have similar A, B and C helices forming a 3-helix bundle, N- and C-terminal tails, and their chains interactions reactions with nucleotides share similarities.
References: https://www.yeastgenome.org/locus/s000005160 DOI: 10.2741/4429 and 10.1016/s0092-8674(00)81088-0
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