XENOPUS TFIIIA GENE-TRANSCRIPTION IS DEPENDENT ON CIS-ELEMENT POSITIONING AND CHROMATIN STRUCTURE

The Xenopus TFIIIA gene is transcribed very efficiently in oocytes. In addition to a TATA element at -30, we show that from -425 to +7 the T FIIIA gene contains only two positive cis elements centered at -267 (e lement 1) and -230 (element 2). This arrangement of the cis elements i n the TFIIIA gene is striking because these two elements are positione d very close to each other yet separated from the TATA element by appr oximately 190 nucleotides. We show that the 190-nucleotide spacing bet ween the TATA element and the upstream cis elements (elements 1 and 2) is critical for efficient transcription of the gene in oocytes and th at a nucleosome is positioned in this intervening region. This nucleos ome may act positively on TFIIIA transcription in oocytes by placing t ranscription factors bound at elements I and 2 in a favorable position relative to the transcription complex at the TATA element.