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.