Description:
CLIP-Cell™Block(bromothenylcytosine,BTC)isanon-fluorescentcompoundthatblocksthereactivityoftheCLIP-tag™invitroandinsideoronthesurfaceoflivingcells.ItcanbeusedtogenerateinactivecontrolsinlivecelllabelingexperimentsperformedwithCLIP-tagfusionproteins.BTCreactswithCLIP-tagirreversIBLy,inactivatingitforsubsequentlabelingsteps.
TheCLIP-tagproteinlabelingsystemenablesthespecific,covalentattachmentofvirtuallyanymoleculetoaproteinofinterest.CLIP-tagisaproteintagbasedonhumanO6-alkylguanine-DNAalkyltransferase(hAGT).CLIP-tagsubstratesarederivativesofbenzylcytosine(BC).Inthelabelingreaction,thesubstitutedbenzylgroupofthesubstrateiscovalentlyattachedtothereactivecysteineofCLIP-tagformingastablethioetherbond. AlthoughCLIP-tagisbasedonthesameproteinasSNAP-tag®,thebenzylcytosinesubstratesformaseparateclassofsubstrates,differentfromthebenzylguaninesubstratesrecognizedbySNAP-tag.CLIP-tagandSNAP-tagcanbeusedfororthogonalandcomplementarylabelingoftwoproteinssimultaneouslyinthesamecells.
Therearetwostepstousingthissystem:subcloningandexpressionoftheproteinofinterestasaCLIP-tagfusion,andlabelingofthefusionwiththeCLIP-tagsubstrateofchoice.TheuseofBTCduringthelabelingoffusionproteinswithCLIP-Cellsubstratesisdescribedinthisdocument.
Notes:
Storage:CLIP-CellBlockshouldbestoredat-20°C(longterm)orat4°C(shortterm).Withproperstorageat-20°C,CLIP-CellBlockisstableforatleastthreeyearsdryorforthreemonthswhendissolvedinDMSO.FortroubleshootingpleaserefertotheinstructionssuppliedwithCLIP-Cellproductsasappropriate.Pleasenotethatthereisaconstantturnoverandresynthesisofproteinsinthecell.AfterhavingblockedallexistingCLIP-tagfusionproteinswithinthecell,newCLIP-tagfusionproteinmoleculesmaybesynthesizedinthemeantimeandmaygetlabeledduringincubationwithafluorescentCLIP-tagsubstrate.Thiswillgivetheimpressionthattheblockingwasineffective.Inordertominimizetheseeffectsofproteinsynthesisandproteintransport,cellsmayhavetobetreatedwithcycloheximideandincubationwiththefluorescentCLIP-tagsubstratemayhavetobeperformedat4°C.