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Mol Cell Biol, March 1998, p. 1570-1579, Vol. 18, No. 3
Department of Chemistry and Molecular Biology
Institute, San Diego State University, San Diego, California
92182-1030
Received 12 September 1997/Returned for modification 9 October
1997/Accepted 2 December 1997
Most small nuclear RNAs (snRNAs) are synthesized by RNA polymerase
II, but U6 and a few others are synthesized by RNA polymerase III.
Transcription of snRNA genes by either polymerase is dependent on a
proximal sequence element (PSE) located upstream of position
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Identification and Topological Arrangement of
Drosophila Proximal Sequence Element (PSE)-Binding
Protein Subunits That Contact the PSEs of U1 and U6 Small Nuclear
RNA Genes
40
relative to the transcription start site. In contrast to findings in
vertebrates, sea urchins, and plants, the RNA polymerase specificity of
Drosophila snRNA genes is intrinsically encoded in the PSE sequence itself. We have investigated the differential interaction of
the Drosophila melanogaster PSE-binding protein
(DmPBP) with U1 and U6 gene PSEs. By using a site specific
protein-DNA photo-cross-linking assay, we identified three polypeptide
subunits of DmPBP with apparent molecular masses of 95, 49, and 45 kDa that are in close proximity to the DNA and two additional
putative polypeptides of 230 and 52 kDa that may be integral to the
complex. The 95-kDa subunit cross-linked at positions spanning the
entire length of the PSE, but the 49- and 45-kDa subunits cross-linked
only to the 3' half of the PSE. The same polypeptides cross-linked to both the U1 and U6 PSE sequences. However, there were significant differences in the cross-linking patterns of these subunits at a subset
of the phosphate positions, depending on whether binding was to a U1 or
U6 gene PSE. These data suggest that RNA polymerase specificity is
associated with distinct modes of interaction of DmPBP with
the DNA at U1 and U6 promoters.
*
Corresponding author. Mailing address: Department of
Chemistry, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182-1030. Phone: (619) 594-5575. Fax: (619) 594-4634. E-mail: wstumph{at}sciences.sdsu.edu.
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