Synergy between theNF-E1Erythroid-Specif ic Transcription Factor andtheCACCC Factor intheErythroid-Specif ic Promoter ofthe HumanPorphobilinogen Deaminase Gene

(to about 12% of the wild-type activity, com-pared with 5% for the promoterless hGH vector alone);mutating the CACCCmotifto GGGCCor deleting a 24-bpfragment containing the CACCCmotif had a similar effect(Table 2). Both the NF-El-binding site and the CACCCmotifare therefore essential for promoteractivity.