6 ) ▁and ▁ob lique ▁( p 2 ) ▁symmetry , ▁for ▁M . ▁ac et iv or ans ▁and ▁G . ▁ste ar oth erm oph ilus ▁S - layers , ▁respectively , ▁and ▁their ▁mole cular ▁features , ▁including ▁dimensions ▁and ▁por os ity , ▁are ▁in ▁good ▁agreement ▁with ▁data ▁from ▁electron ▁micro sc opy ▁studies ▁of ▁arch ae al ▁and ▁b acter ial ▁S - layers . ▁ ▁In ▁general , ▁S - layers ▁exhib it ▁either ▁an ▁ob lique ▁( p 1 , ▁p 2 ), ▁square ▁( p 4 ) ▁or ▁hex ag onal ▁( p 3 , ▁p 6 ) ▁lattice ▁symmetry . ▁Depending ▁on ▁the ▁lattice ▁symmetry , ▁each ▁morph ological ▁unit ▁of ▁the ▁S - layer ▁is ▁composed ▁of ▁one ▁( p 1 ), ▁two ▁( p 2 ), ▁three ▁( p 3 ), ▁four ▁( p 4 ), ▁or ▁six ▁( p 6 ) ▁identical ▁protein ▁sub un its . ▁The ▁center - to - center ▁spacing ▁( or ▁unit ▁cell ▁dimensions ) ▁between ▁these ▁sub un its ▁range ▁from ▁ 4 ▁to ▁ 3 5   nm . ▁ ▁Self - assembly ▁ ▁In ▁v ivo ▁assembly ▁ ▁Assembly ▁of ▁a ▁highly ▁ordered ▁coh er ent ▁mon om ole cular ▁S - layer ▁array ▁on ▁a ▁growing ▁cell ▁surface ▁requires ▁a ▁continuous ▁synth esis ▁of ▁a ▁sur plus ▁of ▁S - layer ▁prote ins ▁and ▁their ▁trans location ▁to ▁sites ▁of ▁lattice ▁growth . ▁Moreover , ▁information ▁concerning ▁this ▁dynamic ▁process ▁were