IDENTIFICATION OF PREVIOUSLY UNRECOGNIZED COMMON ELEMENTS IN EUKARYOTIC PROMOTERS - A RIBOSOMAL-RNA GENE INITIATOR ELEMENT FOR RNA-POLYMERASE-I

A new ribosomal RNA promoter element with a functional role similar to the RNA polymerase II initiator (Inr) was identified, This sequence, which we dub the ribosomal Inr (rInr) is unusually conserved, even in normally divergent RNA polymerase I promoters. It functions in the rec ruitment of the fundamental, TATA-binding protein (TBP)-containing tra nscription factor, TIF-IB. All upstream elements of the exceptionally strong Acanthamoeba castellanii ribosomal RNA core promoter, to within 6 base pairs of the transcription initiation site (tis), can be delet ed without loss of specific transcription initiation, Thus, the A. cas tellanii promoter can function in a manner similar to RNA polymerase I I TATA-less promoters, Sequence-specific photo-cross-linking localizes a 96-kDa subunit of TIF-IB and the second largest RNA polymerase I su bunit (A(133)) to the rInr sequence. A(185) also photo-cross-links whe n polymerase is stalled at +7.