text: Yo, listen up, gotta drop some knowledge on ya
  About the Cdc6 protein, the DNA replication initiator
  It's key to keep that S-phase checkpoint intact
  Anchoring the Rad3-Rad26 complex, that's a fact
  
  But check it, ATR, that's AT mutated and Rad3 related
  It's essential, keeps Cdc6 levels elevated
  When HeLa cells face hydroxyurea-induced arrest
  ATR keeps 'em in check, delayin' mitosis, it's the best
  
  Downregulatin' ATR with ATR-siRNA, you see
  Reduces chromatin Cdc6, that's the key
  Phospho-histone H3 levels shoot up, they rise
  An index of mitosis, no surprise
  
  But hold up, don't stress, there's a solution in sight
  Pretreat with MG132, a proteasome inhibitor, that's right
  Cdc6 levels bounce back, they're restored
  And the entry to mitosis? It's significantly ignored
  
  ATR kinase, it's got a role to play
  Phosphorylates Cdc6 at serine residue 6, okay?
  This ATR-mediated phosphorylation, it's the key
  Stabilizin' Cdc6, keepin' levels high, you see
  
  This whole mechanism, it's novel and tight
  Regulatin' chromatin Cdc6, delayin' the cell cycle's flight
  When hydroxyurea hits, S-phase checkpoint's the guard
  Thanks to ATR and Cdc6, mitosis stays barred