Functional, developmental]) ' expressed genes for mouse Ula and Ulb snRNAs contain both conserved and non-conserved transcription signals

Four genes that encode mouse Ulal, Ulb2 and Ulb6 snRNAs have been isolated from a mouse genomic DNA library. They all appear to be functional Ul genes since they are accurately transcribed into full length, capped snRNAs upon injection into Xenopus oocytes. A mouse pseudogene that is not tran-scribed in Xenopus oocytes was also isolated from the mouse genomic library. DNA sequence analysis of the 5 ' and 3 ' flanking regions of the functional genes revealed the presence of three highly conserved sequence elements that have been shown to be required for transcription initiation or 3 ' end forma-tion in other Ul genes. Each of these Ul RNA genes also contains non-conserved sequences in the 5 ' flanking region that could function in their controlled expression during development