▁ 5 ' ▁over hang s ▁on ▁the ▁DNA ▁called ▁stick y ▁ends : ▁▁ 5 '- A ▁▁▁▁▁▁▁▁ ▁| A ▁G ▁C ▁T ▁T - 3 ' ▁▁ 3 '- T ▁T ▁C ▁G ▁A | ▁▁▁▁▁▁▁▁ ▁A - 5 ' ▁ ▁Rest riction ▁end on uc leases ▁are ▁used ▁as ▁defense ▁mechan isms ▁in ▁pro k ary otic ▁organ isms ▁in ▁the ▁restriction ▁modification ▁system . ▁ ▁Their ▁primary ▁function ▁is ▁to ▁protect ▁the ▁host ▁gen ome ▁against ▁invasion ▁by ▁foreign ▁DNA , ▁primarily ▁b acter i oph age ▁DNA . ▁ ▁There ▁is ▁also ▁evidence ▁that ▁suggests ▁the ▁restriction ▁en zym es ▁may ▁act ▁alongside ▁modification ▁en zym es ▁as ▁self ish ▁elements , ▁or ▁may ▁be ▁involved ▁in ▁gen etic ▁recom bin ation ▁and ▁trans position . ▁ ▁En zym e ▁Str ucture ▁ ▁The ▁structure ▁of ▁H ind III ▁is ▁complex , ▁and ▁consists ▁of ▁a ▁hom od imer . ▁ ▁Like ▁other ▁type ▁II ▁restriction ▁end on uc leases , ▁it ▁is ▁believed ▁to ▁contain ▁a ▁common ▁struct ural ▁core ▁compr ising ▁four ▁ β - sheets ▁and ▁a ▁single ▁α - hel ix . ▁ ▁Each ▁sub unit ▁contains ▁ 3 0 0 ▁am ino ▁ac ids ▁and ▁the ▁predicted ▁mole cular ▁mass ▁is ▁ 3 4 , 9 5 0 ▁Da . ▁ ▁Despite ▁the ▁importance ▁of ▁this ▁en zym e ▁in ▁mole cular ▁bi ology ▁and ▁DNA ▁technology , ▁little ▁information ▁is ▁available ▁concerning ▁the ▁mechanism ▁of ▁DNA ▁recognition ▁and ▁ph osph odi ester