The Bidirectional Promoter of the Divergently Transcribed Mouse Surf-1 and Surf-2 Genes

Abstract

The ubiquitously expressed mouse Surf-1 and Surf-2 genes are divergently transcribed, and their heterogenous start sites are separated by up to a maximum of only 73 bp. By using in vitro DNase I, dimethyl sulfate methylation, and gel retardation assays, we have identified five putative promoter control elements between and around the Surf-1 and Surf-2 start sites. The effects of each site on the regulation of Surf-1 and Surf-2 transcription have been studied in vivo, and four sites were found to be functional promoter elements. A novel binding site is required for efficient use of the intermediate but not the major start site of Surf-1. Three elements function in a bidirectional manner and are shared for efficient and accurate expression of both Surf-1 and Surf-2. One is an UEF (USF, MLTF) binding site which had a small effect on the use of the intermediate start sites of Surf-1 and also affected the major start sites of Surf-2. Another has sequence homology to the RPGα binding site associated with some ribosomal protein gene promoters and is required for efficient expression of the major but not intermediate start sites of Surf-1 and all start sites of Surf-2. The third, an RPGα-like site, is used for all start sites of both Surf-1 and Surf-2. Dissection of this cellular promoter region showed that different binding sites affect the use of different start sites and revealed a complex interaction between multiple elements that constitute a bona fide bidirectional promoter.