The expression of two mouse U1b-2 genes has been studied both in vivo, using DNA transfection experiments, and in vitro using isolated nuclei active in snRNA synthesis. The 5' flanking sequences of the two mouse U1b-2 genes were determined and regions conserved among mammalian U1 genes identified. The 5' flanking sequences of the U1b genes are very similar to a previously reported rat U1a gene suggesting a close evolutionary relationship between the two genes. A promoter element, located between positions -201 and -228, was identified by stable transformation of mouse L cells and CHO cells, which normally express U1b, with cloned U1b-2 genes containing different lengths of 5' flanking sequence. Additional flanking sequences are required for efficient expression of U1b-2 genes in mouse C127 fibroblasts, which normally do not express U1b RNAs. In addition, the changes in the expression of U1b-2 and U1a RNAs was measured in early mouse embryogenesis. / The efficient synthesis U1, U2, and U3 snRNAs was demonstrated in isolated mouse myeloma nuclei. Accurate initiation of U1 RNA was shown to occur in this system by using (beta)-thionucleotides in the transcription reaction. There was no transcription upstream of the U1b gene but two classes of transcripts with 3' extensions were observed. Transcripts with 3-5 base 3' extensions were released from nuclei and trimmed to the mature size in vitro. In contrast, the transcripts with 200-300 base extensions were retained in nuclei and not processed to the mature size, suggesting that 3' end formation is normally coincident with transcription. / Source: Dissertation Abstracts International, Volume: 48-03, Section: B, page: 0659. / Thesis (Ph.D.)--The Florida State University, 1987.

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