U3 snoRNA promoter reflects the RNA's function in ribosome biogenesis

An efficiently expressed tagged gene system was used to study promoter sequence elements in genes encoding the U3 snoRNAs of Schizosaccharomyces pombe. Transcription was found dependent on two previously thought, mutually exclusive elements, a TATA-box, as found in other S. pombe snRNA gene promoters, and a Homol D-box, often considered a TATA-box analogue in the promoters of genes that encode ribosomal proteins. The Homol D-box is critical while the TATA-box strongly influences transcription efficiency but is not essential. The results suggest that the U3 snoRNA promoter may represent the fusion of two promoter systems reflecting the special role of this RNA in ribosome biogenesis. Steady state measurements of cellular RNAs support such a coordinated regulation of the U3 snoRNA.