▁element ▁surrounding ▁the ▁origin ▁of ▁rep lication ▁direct s ▁trans cription , ▁and ▁T - ant igen ▁direct s ▁trans cription ▁and ▁rep lication . ▁ ▁SV 4 0 ▁DNA ▁rep lication ▁is ▁initi ated ▁by ▁binding ▁of ▁large ▁T - ant igen ▁to ▁the ▁origin ▁region ▁of ▁the ▁gen ome . ▁The ▁function ▁of ▁T - ant igen ▁is ▁controlled ▁by ▁ph osph ory lation , ▁which ▁at ten u ates ▁the ▁binding ▁to ▁the ▁SV 4 0 ▁origin . ▁Prote in - prote in ▁interactions ▁between ▁T - ant igen ▁and ▁DNA ▁polym er ase - alpha ▁directly ▁stim ulate ▁rep lication ▁of ▁the ▁virus ▁gen ome . ▁ ▁T - ant igen ▁also ▁bind s ▁and ▁in activ ates ▁tum or ▁suppress or ▁prote ins ▁( p 5 3 , ▁p 1 0 5 - R b ). ▁This ▁causes ▁the ▁cells ▁to ▁leave ▁G 1 ▁phase ▁and ▁enter ▁into ▁S ▁phase , ▁which ▁prom otes ▁DNA ▁rep lication . ▁ ▁The ▁SV 4 0 ▁gen ome ▁is ▁very ▁small ▁and ▁does ▁not ▁encode ▁all ▁the ▁information ▁necessary ▁for ▁DNA ▁rep lication . ▁Therefore , ▁it ▁is ▁essential ▁for ▁the ▁host ▁cell ▁to ▁enter ▁S ▁phase , ▁when ▁cell ▁DNA ▁and ▁the ▁vir al ▁gen ome ▁are ▁rep licated ▁together . ▁Therefore , ▁in ▁addition ▁to ▁increasing ▁trans cription , ▁another ▁function ▁of ▁T - ant igen ▁is ▁to ▁alter ▁the ▁cell ular ▁environment ▁to ▁permit ▁virus ▁gen ome ▁rep lication . ▁ ▁N uc lear ▁local ization ▁signal ▁