TRANSCRIPTION OF SATELLITE 2-DNA FROM THE NEWT IS DRIVEN BY A SNRNA TYPE OF PROMOTER

The transcriptional promoter of satellite 2 from the eastern newt, Notophthalmus viridescens, was analyzed by assaying the activity of deleted or mutated satellite 2 clones in Xenopus laevis oocytes. Two elements in the promoter were found to be important for transcription. These elements have sequences that are similar to the sequences of the octamer and the proximal sequence element of vertebrate snRNA genes transcribed by RNA polymerase II. Furthermore, the organization of these elements and their respective roles in transcription are the same as their organization and roles in the snRNA genes. To further investigate the relationship between the satellite 2 and snRNA gene promoters, the ability of the satellite 2 promoter to drive transcription of a true snRNA gene was tested. The satellite 2 promoter initiated transcription of the Xenopus U1b2 snRNA ge:ne as efficiently as the native U1b2 promoter, and the 3' ends of the resulting U1b2 transcripts were accurately formed. This latter result confirms that the satellite 2 promoter is a functional analog of the snRNA promoter, since 3'-end formation of snRNA genes transcribed by RNA polymerase II requires that transcription be initiated from a compatible promoter. The structural and functional similarities between the satellite 2 and the snRNA gene promoters suggest that these elements are evolutionarily related. These findings were used to extend a previously proposed model concerning the nature and derivation of satellite 2.