When the embryo has functional testes, Leydig cells of the fetal testis secrete testosterone, and the Sertoli cells secrete MIS (MRF)

#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.

#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.

#Id: 6004

#Unit 3. Fundamental Processes

#Id: 6005

#Unit 3. Fundamental Processes

Orc2-5 binds strongly; Orc6 binds weakly to ARS and has a nuclear localization signal that must be activated by the cyclin/ CDK kinase during the G1 to S transition.

#Id: 6006

#Unit 3. Fundamental Processes

ATP is required for the binding, but is not hydrolyzed until a later stage. The transcription factor ABF1 binds to the B3 element; this assists initiation by affecting chromatin structure, but it is the events that occur at the A and B1 elements that actually cause initiation

#Id: 6007

#Unit 3. Fundamental Processes

Most origins are localized in regions between genes, which suggests that it may be important for the local chromatin structure to be in a nontranscribed condition.