Abstract: GUS gene controlled by different regulator sequences (CaMV35S promoter, Ubi.U4 promoter and Kozak sequence) were introduced into the leaves of tobacco. Transient expression assay revealed a 2-fold increase in GUS activity in leaves with GUS expression driven by the CaMV35S promoter fused to the Kozak sequence (pSKG) as compared with the pBI121. The expression of GUS driven by a double CaMV35S promoter with the Kozak sequence was not significantly different from that driven by the single CaMV35S promoter with the Kozak sequence. Expression with the Ubi.U4 promoter with the Kozak sequence of pUKG yielded about a 1.5-fold higher level of GUS activity than expression with the CaMV35S promoter with the Kozak sequence. The tandem Ubi.U4-CaMV35S promoter with the Kozak sequence was the most effective among the regulator sequences and gave a 3-fold higher expression level than that driven by the double CaMV35S promoter with the Kozak sequence and a 10-fold higher expression level than that driven by the single CaMV35S promoter.