Orc1 Background Information Orc1 and Orc2 (also designated RRR1 or SIR5) are two of the six subunits that compose the yeast origin of replication complex (Orc). This complex binds to autonomously replicating sequences (ARS) and serves as an initiator protein for DNA replication. The minichromosome maintenance (MCM) proteins also play an essential role in regulating DNA replication by binding to chromatin and activating the ORC-ARS complex. Cdc6, involved in limiting DNA replication to once per cell cycle, binds to the ORC and is essential for the assembly of the MCM proteins. The transcription factor Abf1 (also des-ignated Obf1 or Baf1) also binds to the ARS and plays a role in gene silencing as well as in DNA replication.
