challenge: What is the primary function of the protein encoded by the UHRF1 gene during S-phase?
  
  A. To bind to hemi-methylated DNA and recruit the main DNA methyltransferase protein, DNMT1
  B. To bind to fully methylated DNA and recruit histone modifying enzymes
  C. To regulate cell cycle progression by interacting with p53
  D. To phosphorylate topoisomerase 2a
  Answer: 