A single base pair deletion from the inactive octamer-like motif of the 7S K distal sequence element brings full functionality in vivo.

Octamer sequence elements were analyzed for their capacity to induce the 7S K "core" promoter in vivo. The U6 distal sequence element (DSE) which contains a consensus sequence octamer, was able to support efficient 7S K expression in vivo. In contrast, no such function could be attributed to the octamer-like element alone, which is present within the 7S K DSE. However, conversion of this octamer-like element (ATTTaGCAT) to the octamer consensus sequence ATTTGCAT generated a potent DSE, even in the absence of the CACCC box, which constitutes the major functional element of the 7S K DSE. Both the consensus and the octamer-like sequences revealed no cooperativity with the CACCC box. Together, these results demonstrate that the octamer-like element of the wild-type 7S K DSE is definitely not functional in vivo. Furthermore, our experiments indicate that in contrast to the RNA polymerase II-transcribed small nuclear RNA genes, in intact cells a single functional DSE motif is necessary and sufficient for maximal transcription by RNA polymerase III of the 7S K RNA gene.