J. Biol. Chem., Vol. 265, Issue 17, 9728-9731, Jun, 1990
Site-directed mutational analysis of a U4 small nuclear RNA gene proximal sequence element. Localization and identification of functional nucleotides
KJ McNamara and WE Stumph
Department of Chemistry, San Diego State University, California 92182- 0328.
The genes that encode the small nuclear RNAs (snRNAs) are unusual RNA
polymerase II transcription units in that 5'-flanking DNA sequences more
than 50 base pairs upstream of snRNA genes are essential for specifying the
transcription initiation site. The relevant cis-acting DNA sequence, termed
the proximal sequence element (PSE), is required for both transcription
initiation and 3'-end formation of snRNAs. We have used site-directed
mutagenesis and expression in Xenopus oocytes to map nucleotides important
for the function of the chicken U4B snRNA gene PSE. The results indicate
that nucleotide sequences upstream of position -65 are not required for U4B
PSE activity. However, nucleotides lying within a region 53-65 base pairs
upstream of the U4B gene are essential for obtaining a detectable level of
U4B gene expression. Six nucleotides between positions -53 and -59 were
identified at which base substitutions reduced the transcriptional activity
of the U4B gene.