Cloning and identification of the pig ribosomal gene promoter.

Pig ribosomal RNA-encoding gene (rDNA) clones were obtained by screening a pig genomic DNA library. A 742-bp segment containing the promoter was sequenced. Using total pig RNA, the tsp (transcription start point) was defined by primer extension. A promoter-like region was found immediately upstream from the active promoter. Promoter function was studied by transfection of pig tissue culture cells and assayed by a highly sensitive RT-PCR method. Alignment of five mammalian rDNA promoter sequences, human, mouse, rat, rabbit and pig, showed five conserved subregions which may be important in transcriptional regulation. An unusual feature of the pig rDNA promoter is that instead of a G at -16, which is conserved in eukaryotes, there is a C.