Ricerc@Sapienza

S. cerevisiae ribosomal DNA (rDNA) locus hosts a series of highly complex regulatory machineries for RNA polymerase I, II and III transcription, DNA replication and units recombination, all acting in the Non Transcribed Spacers (NTSs) interposed between the repeated units by which it is composed. DNA topoisomerase I (Top1p) contributes, recruiting Sir2p, to the maintenance of transcriptional silencing occurring at the RNA Polymerase II cryptic promoters, located in the NTS region.

Saccharomyces cerevisiae ribosomal DNA, the repeated region where rRNAs are synthesized by about 150 encoding units, hosts all the protein machineries responsible for the main DNA transactions such as replication, transcription and recombination. This and its repetitive nature make rDNA a unique and complex genetic locus compared to any other. All the different molecular machineries acting in this locus need to be accurately and finely controlled and coordinated and for this reason rDNA is one of the most impressive examples of highly complex molecular regulated loci.