Immunogen sequence: LDELESSDLP VALLLAQHKD RSTQLEMQLE KPKPVKPVTF STGIKMGQHI SLAPIHKLEE ALYEYQPLQI ETYGPHVPEL EMLGRLGYLN HVRAASPQDL AG. Progression through the cell cycle requires activation of a series of enzymes designated cyclin dependent kinases (Cdks)