▁util izes ▁a ▁catal yt ically ▁in active ▁nuc lease ▁to ▁phys ically ▁block ▁R NA ▁polym er ase , ▁ ▁effectively ▁prevent ing ▁or ▁hal ting ▁trans cription . ▁P ert urb - seq ▁has ▁been ▁util ized ▁with ▁both ▁the ▁knock out ▁and ▁CR IS PR i ▁approaches ▁in ▁the ▁D ix it ▁et ▁al . ▁paper ▁ ▁and ▁the ▁Adam son ▁et ▁al . ▁paper , ▁respectively . ▁ ▁Pool ing ▁all ▁guide ▁R N As ▁into ▁a ▁single ▁screen ▁re lies ▁on ▁DNA ▁bar codes ▁that ▁act ▁as ▁ident ifiers ▁for ▁each ▁unique ▁guide ▁R NA . ▁There ▁are ▁several ▁commer cially ▁available ▁po o led ▁CR IS PR ▁libraries ▁including ▁the ▁guide ▁bar code ▁library ▁used ▁in ▁the ▁study ▁by ▁Adam son ▁et ▁al . ▁CR IS PR ▁libraries ▁can ▁also ▁be ▁custom ▁made ▁using ▁tools ▁for ▁s g R NA ▁design , ▁many ▁of ▁which ▁are ▁listed ▁on ▁the ▁CR IS PR / cas 9 ▁tools ▁Wikipedia ▁page . ▁ ▁L ent iv iral ▁vectors ▁▁ ▁The ▁s g R NA ▁expression ▁vector ▁design ▁will ▁depend ▁largely ▁on ▁the ▁experiment ▁performed ▁but ▁requires ▁the ▁following ▁central ▁components : ▁▁ ▁Prom oter ▁ ▁Rest riction ▁sites ▁ ▁Pr imer ▁Binding ▁S ites ▁ ▁s g R NA ▁ ▁Guide ▁Bar code ▁ ▁Re porter ▁gene : ▁ ▁Fl u ores cent ▁gene : ▁vectors ▁are ▁often ▁constructed ▁to ▁include ▁a ▁gene ▁encoding ▁a ▁flu ores cent ▁protein , ▁such ▁that ▁successfully ▁trans du ced ▁cells ▁can ▁be ▁vis