An unusually compact external promoter for RNA polymerase III transcription of the human H1RNA gene

H1 RNA, the RNA component of the human nuclear RNase P, is encoded by a uni que gene transcribed by RNA polymerase III (Pol III). In this work, cis-act ing elements and trans-acting factors involved in human H1 gene transcripti on were characterized by transcription assays of mutant templates and DNA a ssays of recombinant proteins. Four elements, lying within 100 bp of 5'-fla nking sequences, were defined to be essential for maximal in vitro and in v ivo expression, consisting of the octamer, Staf, proximal sequence element (PSE) and TATA motifs. These are also encountered in the promoter elements of vertebrate snRNA genes, where the first two constitute the distal sequen ce element (DSE). In all the genes examined so far, the DSE is distant from the PSE and TATA box that compose the basal promoter. However, we observed a fundamental difference in the organization of the H1 RNA and snRNA gene promoters with respect to the relative spacing of the DSE and PSE. Indeed, the H1 promoter is unusually compact, with the octamer motif and Staf bindi ng site adjacent to the PSE and TATA motifs. It thus appears that the human RNase P RNA gene has adopted a unique promoter strategy placing the DSE im mediately adjacent to the basal promoter.