The G1 cyclin-CDK complex (Cln3-CDK in yeast) stimulates the formation of G1/S phase cyclin-CDKs, which initiate bud formation, centrosome duplication, and DNA replication.

TLS Online TPP Program

#Id: 5998

#Unit 3. Fundamental Processes

An ARS element consists of an A-T–rich region that contains discrete sites in which mutations affect origin function.

TLS Online TPP Program

#Id: 5999

#Unit 3. Fundamental Processes

A 14-bp “core” region, called the A domain, which contains an 11-bp consensus sequence consisting of A-T base pairs. This consensus sequence (sometimes called the ACS, for ARS)

TLS Online TPP Program

#Id: 6000

#Unit 3. Fundamental Processes

The origin recognition complex (ORC) is a highly conserved complex found in all eukaryotes.  It is composed of six proteins with a mass of 400 kD.  ORC binds to the yeast A and B1 elements on the A-T–rich strand and is associated with ARS elements throughout the cell cycle.

TLS Online TPP Program

#Id: 6001

#Unit 3. Fundamental Processes

By counting the number of sites to which ORC binds, we can estimate that there are about 400 origins of replication in the yeast genome. This means that the average length of a replicon is 35,000 bp.

TLS Online TPP Program

#Id: 6002

#Unit 3. Fundamental Processes

ORC was first found in S. cerevisiae (where it may be called scORC), but similar complexes have now been characterized in Schizosaccharomyces pombe (spORC), Drosophila (DmORC), and Xenopus (XlORC). All of the ORC complexes bind to DNA.

TLS Online TPP Program

#Id: 6003

#Unit 3. Fundamental Processes

A eukaryotic genome is divided into multiple replicons, and the origin in each replicon is activated once and only once in a single division cycle.