▁in ▁ 2 0 0 4 ▁ ▁and ▁GC a MP ▁was ▁subsequently ▁improved ▁to ▁GC a MP 2 , ▁which ▁was ▁stable ▁at ▁m amm al ian ▁body ▁temper atures ▁and ▁enabled ▁the ▁first ▁in ▁v ivo ▁m amm al ian ▁record ings ▁using ▁a ▁G E CI . ▁ ▁GC a MP s ▁have ▁been ▁subsequently ▁modified ▁to ▁progress ively ▁improve ▁the ▁range ▁of ▁the ▁flu ores c ence ▁signal , ▁resulting ▁in ▁GC a MP 3 ▁through ▁GC a MP - X . ▁ ▁Additionally , ▁red ▁flu ores c ence ▁G EC Is , ▁term ed ▁" RC a MP s " ▁have ▁been ▁developed ▁to ▁expand ▁the ▁spectral ▁options ▁for ▁multi - line age ▁imag ing . ▁▁ ▁G FP ▁is ▁circular ly ▁permut ated ▁so ▁that ▁the ▁N - ▁and ▁C - termin i ▁are ▁f used , ▁creating ▁a ▁new ▁termin us ▁in ▁the ▁middle ▁of ▁the ▁protein . ▁F used ▁to ▁the ▁new ▁termin us ▁is ▁cal mod ul in ▁( Ca M ) ▁and ▁the ▁M 1 3 ▁domain ▁of ▁a ▁my os in ▁light ▁chain ▁kin ase . ▁Cal mod ul in ▁is ▁a ▁symmet rical , ▁h inge - like ▁protein ▁that ▁bind s ▁to ▁four ▁calci um ▁ ions ▁via ▁E - F ▁mot ifs . ▁When ▁calci um ▁is ▁present , ▁Ca M ▁under go es ▁a ▁conform ational ▁change , ▁and ▁the ▁h inge ▁region ▁is ▁able ▁to ▁bind ▁hel ical ▁pe pt ide ▁ch ains ▁on ▁target ▁prote