Functional elements of the human U1 RNA promoter. Identification of five separate regions required for efficient transcription and template competition.

We have determined the structure of the human U1 snRNA promoter by microinjection of several mutant U1 templates into Xenopus laevis oocytes. These deletion templates were assayed for their ability to express mature U1 RNA and for their ability to compete for limiting transcription factors. We have mapped five separate regions, called promoter elements A, B, C, D, and E. Element A, located between positions -8 and -50, stimulates transcription 3- to 5-fold increases the accuracy of initiation; element B (between -50 and -80) fixes the site of initiation and stimulates transcription greater than 100-fold; element C (upstream of -129) increases the efficiency of element B 3- to 5-fold; element D (between -191 and -231) is an orientation-independent and partially position-independent enhancer responsible for a 100-fold stimulation of transcription; element E (between -335 and -393) increases the ability to compete with other snRNA genes 4-fold. All five promoter elements are required for effective competition with the wild-type U1 promoter suggesting that binding of transcription factor(s) to the complex is cooperative. The U1 RNA and some mRNA gene transcription complexes appear to share one or more transcription factors.