▁is o form , ▁with ▁long ▁signal ▁pe pt ide ▁of ▁ 4 8 ▁am ino ▁ac ids ▁( IL - 1 5 ▁L SP ) ▁consisted ▁of ▁a ▁ 3 1 6 ▁b p ▁ 5 ’ - un trans l ated ▁region ▁( UT R ), ▁ 4 8 6 ▁b p ▁coding ▁sequence ▁and ▁the ▁C - ter minus ▁ 4 0 0 ▁b p ▁ 3 ’ - UT R ▁region . ▁The ▁other ▁is o form ▁( IL - 1 5 ▁S SP ) ▁has ▁a ▁short ▁signal ▁pe pt ide ▁of ▁ 2 1 ▁am ino ▁ac ids ▁encoded ▁by ▁ex ons ▁ 4 A ▁and ▁ 5 . ▁Both ▁is o forms ▁shared ▁ 1 1 ▁am ino ▁ac ids ▁between ▁ ▁signal ▁sequences ▁of ▁the ▁N - ter minus . ▁Although ▁both ▁is o forms ▁produce ▁the ▁same ▁m ature ▁protein , ▁they ▁differ ▁in ▁their ▁cell ular ▁tra ff ick ing . ▁IL - 1 5 ▁L SP ▁is o form ▁was ▁identified ▁in ▁Gol gi ▁appar atus ▁[ GC ], ▁early ▁end os om es ▁and ▁in ▁the ▁end op las mic ▁ret icul um ▁( ER ). ▁It ▁exists ▁in ▁two ▁forms , ▁secret ed ▁and ▁memb rane - bound ▁particularly ▁on ▁d end rit ic ▁cells . ▁On ▁the ▁other ▁hand , ▁IL - 1 5 ▁S SP ▁is o form ▁is ▁not ▁secret ed ▁and ▁it ▁appears ▁to ▁be ▁restricted ▁to ▁the ▁cy top las m ▁and ▁nucle us ▁where