COMPLEX REQUIREMENTS FOR RNA POLYMERASE-III TRANSCRIPTION OF THE XENOPUS U6 PROMOTER

The role of various sequences in determining the RNA poIymerase III (poI III) specificity of the Xenopus U6 gene promoter has been investigated. A sequence closely resembling an RNA poIymerase II (poI II) TATA box, which has previously been implicated in determining the poI III specificity of the U6 promoter, was analyzed in detail. The U6 TATA-like element, in a different promoter context, is shown to be capable of mediating RNA poIymerase II transcription both in vitro and in oocyte microinjection experiments. Extensive mutagenesis of the TATA-like element in the context of the poI III and poI II promoters leads to the conclusion that the sequence requirements for function in the two contexts are dissimilar, suggesting that different factors may be involved in mediating poI II and poI III transcription. Further, as implied by the above results, it is shown that the poIymerase III specificity of the U6 gene is not solely dependent upon the TATA-like element but rather reflects complex interaction between multiple components of the promoter. © 1990 Oxford University Press.