The 5' flanking (promoter) region of the Arabidopsis thaliana cdc2a gene was cloned and sequenced. A number of putative regulatory motifs were identified including one Myc and three Myb protein binding sequences plus one abscisic acid and two auxin responsive elements. One of the three Myb protein binding sequences is positioned within an auxRE. Promoter-GUS fusions were introduced into plants to study the role of two promoter regions in regulating gene expression. Absence of one Myb binding sequence and the auxRE containing a Myb binding sequence resulted in a significant reduction in expression levels as did a deletion involving the Myc and the third Myb binding sequences along with the second auxRE. However, no changes in expression patterns were observed. The results were quantified using transgenic root cultures.