Negative effect of the 5 '-untranslated leader sequence on Ac transposon promoter expression

Transposable elements are used in heterologous plant hosts to clone genes b y insertional mutagenesis. The Activator (Ac) transposable element has been cloned from maize, and introduced into a variety of plants. However, diffe rences in regulation and transposition frequency have been observed between different host plants. The cause of this variability is still unknown. To better understand the activity of the Ac element, we analyzed the Ac promot er region and its 5'-untranslated leader sequence (5' UTL). Transient assay s in tobacco NT1 suspension cells showed that the Ac promoter is a weak pro moter and its activity was localized by deletion analyses. The data present ed here indicate that the core of the Ac promoter is contained within 153 b p fragment upstream to transcription start sites. An important inhibitory e ffect (80%) due to the presence of the 5' UTL was found on the expression o f LUC reporter gene. Here we demonstrate that the presence of the 5' UTL in the constructs reduces the expression driven by either strong or weak prom oters.