Functional regions of the cauliflower mosaic virus 35S RNA promoter determined by use of the firefly luciferase gene as a reporter of promoter activity

Abstract

The cauliflower mosaic virus (CaMV) 35S RNA promoter has been dissected and examined in a transient expression system using the firefly luciferase gene as a reporter of promoter activity. Deletion analysis has shown that the 35S RNA promoter is composed of at least three regions—distal, medial, and proximal—which are essential for activity. The distal region contains three smaller elements homologous to the simian virus 40 “core” enhancer element, the medial region possesses a CCAAT-like box, and the proximal region contains a TATA box. A DNA segment encompassing the distal region is capable of activating the CaMV 35S core promoter in an orientation-independent, but not position-independent, fashion. The distal region can also activate a heterologous weak promoter, the CaMV 19S RNA promoter, albeit not to the high levels of the 35S RNA promoter. Multimers of the distal region are able to activate the 35S RNA promoter core to even greater levels of expression than the native 35S promoter. These experiments demonstrate that elements outside the boundaries of the core promoter (composed of proximal and medial elements) are recognized in a plant cell transient expression system.