TATA box and initiator functions in the accurate transcription of a plant minimal promoter in vitro.

The functional architecture of the proximal region of a rice phenylalanine ammonia-lyase (PAL) promoter was analyzed by transcription of PAL-beta-glucuronidase (GUS) templates by whole-cell extracts of rice cell suspension cultures. The promoter 5' truncated to position -35 was sufficient for accurate initiation of basal transcription. Substitution of the TATTTAA sequence between positions -35 and -28 with GCGGGTT or 2-bp substitutions to give TCGTTAA and TATGGAA inactivated the minimal promoter. Moreover, the function of the TATTTAA sequence was dependent on its position relative to the initiation site; hence, this element is an authentic TATA box essential for RNA polymerase II-dependent transcription. Substitutions in the TCCAAG initiator cis element (-3 to +3) at the -1 (C to A or G) and +1 (A to C or T) residues caused inaccurate initiation, whereas mutations at the other residues of this conserved element or sequence substitutions between the TATA box and initiator had little effect. TATA box and initiator functions were confirmed by analysis of the effects of promoter mutations on expression in stably transformed rice cell suspensions and plants. We concluded that the proximal region of the PAL promoter has a simple functional architecture involving a TATA box appropriately positioned upstream of the initiator. Transcription of derivatives of such minimal promoters by highly active cell extracts should allow molecular analysis of functional interactions between specific cis elements and cognate trans factors.