We studied cis regulatory elements controlling the light-dependent organ-specific expression of Arabidopsis thaliana chlorophyll a/b binding protein gene (cab1) by stably transforming tobacco plants using a tumor-inducing (Ti) plasmid vector system. The results from the 5' and internal deletion analyses indicate that there are at least three cis-acting elements that are involved in the light-dependent developmental expression of cab1 gene. Two such elements are located at the immediate upstream regulatory region and the other element is located at the further upstream region. The 1120-base-pair (bp) DNA fragment containing the immediate and far upstream region can confer light-inducible organ specificity on the truncated nos promoter. However, deletion of the 39-bp DNA fragment at the immediate upstream regulatory region from this hybrid promoter resulted in a nonfunctional promoter, revealing that the 39-bp region is important for the cab promoter specificity. Further analyses of this region suggest that a potential Z-DNA-forming sequence (ATACGTGT) is involved in light-dependent developmental expression of the cab1 gene. Two additional Z-DNA-forming sequences (ACACATAT) that are inverted repeats of this sequence are also found in the upstream region where the additional regulatory elements are expected.