Human genes for U2 small nuclear RNA are tandemly repeated

Abstract

We found that the genes for human U2 small nuclear RNA (snRNA) are organized as a nearly perfect tandem array of 10 to 20 copies per haploid genome. Although the coding region for the mature form of U2 RNA was only 188 base pairs (bp) long, the basic repeating unit of the tandem array was 6 kilobase pairs in length. Comparison of DNA sequences immediately upstream from human U1 and U2 genes revealed two regions of strong homology: region I (15 bp long) lay upstream of region II (20 bp long) and was separated from it by about the same distance in U1 genes (25 bp) as in U2 genes (21 bp); however, region I and region II were located 174 bp further upstream from the 5' end of the snRNA coding sequence in U1 genes than in U2 genes. Homologs of region II were also found upstream of the snRNA coding region in a mouse U2 gene and two rat U1 genes. Murphy et al. (Cell 29:265-274, 1982) have found that sequences within region II may function as the equivalent of a TATA box for initiation by RNA polymerase II in vitro at a position 183 bp upstream from the 5' end of the human U1 snRNA coding region. In light of the data reported here, this result suggests that region II does indeed play a role in transcription but that its position relative to the actual initiation site can vary.