Transcription of a human U6 small nuclear RNA gene in vivo withstands deletion of intragenic sequences but not of an upstream TATATA box.

Most eukaryotic genes transcribed by RNA polymerase III contain internal control regions. U6 small nuclear RNA genes are transcribed by RNA polymerase III but are unusual in that, at least in vitro, their expression does not require intragenic sequences. Here we show that this is true as well in vivo. A human U6 gene devoid of all but the first 6 and last 10 base-pairs was expressed efficiently after transfection into human 293 cells. We also report data extending the previous identification of 5' flanking sequences important for human U6 gene transcription. Deletion-substitution of a 10 base-pair upstream sequence encompassing the TATATA element (-29 to -24) abolished U6 transcription. A double point mutation in the middle of this element (TATATA-TAGCTA) reduced U6 transcription but not to the extent brought about by TATATA deletion-substitution. These results establish that, in vivo, transcription of human U6 small nuclear RNA is independent of intragenic sequences between nucleotides 6 and 98, and requires the upstream TATATA box.