A tobacco cryptic constitutive promoter, tCUP, revealed by T-DNA tagging

We have isolated a constitutive promoter sequence, tCUP, from tobacco by T- DNA tagging using a promoterless GUS-nos3' reporter gene construct. The T-D NA integration event produced a translational fusion with the GUS gene that is expressed widely in organs, at both the mRNA and enzyme activity levels . In tobacco transformed with a tCUP-GUS-nos3' gene, GUS specific activity in leaves was within a range of values similar to those of plants transform ed with the widely used constitutive promoter gene fusion, CaMV 35S promote r-GUS-nos3'. Characteristics of the tCUP promoter sequence differ from thos e of other plant constitutive promoters; for instance, the tCUP sequence la cks a TATA box. Transcription initiates at a single site within the tCUP se quence which is similar to a transcriptional start site consensus sequence determined for plant genes. The tCUP promoter is cryptic as RNA accumulatio n at the transcriptional start site is not detected in untransformed tobacc o. Thus, tCUP is the first example of a cryptic, constitutive promoter isol ated from plants. The tCUP-GUS-nos3' gene fusion produced GUS activity in t issues of all species tested suggesting that tCUP may utilize fundamental t ranscription mechanisms found in plants.