The major histocompatibility complex (MHC) Ea promoter: sequences and factors at the initiation site

We have analysed the function of sequences in the TATA/initiator region of the promoter of Ea, a class II gene of the Major Histocompatibility Complex. We find that the Ea promoter contains an initiator element with a strong influence on transcription. We also find that the Ea promoter does contain a bona fide TATA box, which can be recognized by the TATA binding protein (TBP), and that TBP is required for transcriptional activity. For activity, TBP must be included within a larger TFIID complex, as Ea transcription in a heat-treated extract can be restored by immunopurified TFIID but not by TBP alone. On the other hand, the TATA motif can be eliminated without significantly affecting either the efficiency or the startsites of transcription. This suggests that TBP, even in this TATA-containing promoter, is held in place by other components of the initiation complex, regardless of its affinity for the underlying DNA.