Differential regulation of transcription of human 7 S K and 7 S L RNA genes.

Two functional human genes coding for 7 S RNA species K and L were analyzed for promoter requirements by in vitro transcription experiments with cytoplasmic S-100 extracts. Since accurate and efficient transcription of both genes is dependent on the presence of 5'-flanking sequences, hybrid genes representing crossover fusions between the 5' external control regions and the coding sequences of both genes were analyzed for their capacity to direct RNA synthesis in vitro. Differing results were obtained with both types of constructs. While the 5'-flanking L-7 S K gene fusion revealed no activity in the in vitro transcription assay, the 5'-flanking sequence of the 7 S K RNA gene did confer the ability for accurate in vitro transcription to the 7 S L coding sequence. However, a 5'-flanking L sequence element including the first 22 nucleotides of the 7 S L RNA coding sequence was active in promoting transcription of the 7 S K RNA gene. Together, these results demonstrated that the 7 S L promoter is located inside and outside the coding region, whereas the 7 S K RNA gene is exclusively controlled by an upstream promoter element.