COMMON AND UNIQUE TRANSCRIPTION FACTOR REQUIREMENTS OF HUMAN U1 AND U6 SNRNA GENES

The human U1 and U6 genes have similar basal promoter structures. A fi rst analysis of the factor requirements for the transcription of a hum an U1 gene by RNA polymerase II in vitro has been undertaken, and thes e requirements compared with those of human U6 gene transcription by R NA polymerase III in the same extracts. Fractions containing PSE-bindi ng protein (PBP) are shown to be essential for transcription of both g enes, and further evidence that PBP itself is required for U1 as well as U6 transcription is presented. On the other hand, the two genes hav e distinct requirements for TATA-binding protein (TBP). On the basis o f chromatographic and functional properties, the TBP, or TBP complex, required for U1 transcription appears to differ from previously descri bed complexes required for RNA polymerase I, II or III transcription. The different TBP requirements of the U1 and U6 promoters are reflecte d by specific association with either TFIIB or TFIIIB respectively, th us providing a basis for differential RNA polymerase selection.