or ▁sp lice ▁site ▁on ▁the ▁out ron , ▁and ▁a ▁ 5 ' ▁don or ▁sp lice ▁site ▁( G U ▁din uc le ot ide ) ▁located ▁on ▁a ▁separate ▁R NA ▁mole c ule , ▁the ▁SL ▁R NA . ▁Moreover , ▁the ▁out ron ▁of ▁the ▁prem ature ▁m R NA ▁contains ▁a ▁branch point ▁ad en os ine ▁— ▁followed ▁by ▁a ▁down stream ▁pol yp yr im id ine ▁tract ▁— ▁which ▁interact s ▁with ▁the ▁intr on - like ▁portion ▁of ▁the ▁SL ▁R NA ▁to ▁form ▁a ▁' Y ' ▁branch ed ▁by product , ▁rem in is cent ▁of ▁the ▁l asso ▁structure ▁formed ▁during ▁intr on ▁sp lic ing . ▁N uc lear ▁mach in ery ▁then ▁resol ves ▁this ▁' Y ' ▁branch ing ▁structure ▁by ▁trans - sp lic ing ▁the ▁SL ▁R NA ▁sequence ▁to ▁the ▁ 3 ′ ▁trans - sp lice ▁accept or ▁site ▁( AG ▁din uc le ot ide ) ▁of ▁the ▁pre - m R NA . ▁ ▁When ▁out rons ▁are ▁processed , ▁the ▁SL ▁ex on ▁is ▁trans - sp lic ed ▁to ▁distinct , ▁un pa ired , ▁down stream ▁accept or ▁sites ▁adjacent ▁to ▁each ▁open ▁reading ▁frame ▁of ▁the ▁pol yc ist ron ic ▁pre - m R NA , ▁leading ▁to ▁distinct ▁m ature ▁c apped ▁trans cript s . ▁ ▁See ▁also ▁▁ ▁Ex on ▁ ▁M essen ger ▁R NA ▁ ▁References ▁ ▁Category : Sp lice