CHARACTERIZATION OF A DROSOPHILA PROXIMAL-SEQUENCE-ELEMENT-BINDING PROTEIN INVOLVED IN TRANSCRIPTION OF SMALL NUCLEAR-RNA GENES

In a wide variety of eukaryotic organisms, transcription of small nucl ear RNA (snRNA) genesis dependent upon a proximal sequence element (PS E) located upstream of position -40 relative to the transcription star t site. There is little or no existent knowledge concerning the PSE-bi nding proteins of organisms other than human. Here, we report the puri fication of a fraction enriched in the Drosophila melanogaster PSE-bin ding protein (DmPBP). DmPBP forms a highly specific complex with the P SE. The protein stimulates transcription from the U1 gene promoter by RNA polymerase IT and from the U6 gene promoter by RNA polymerase LII in Drosophila nuclear extracts, and activation is dependent upon the p resence of a PSE. The molecular mass of native DmPBP as measured by ge l-filtration chromatography is 375 kDa. Two polypeptides (apparent mol ecular masses 59 kDa and 61 kDa) appear to be in close contact with th e DNA in that they can be very efficiently and specifically crosslinke d to the PSE sequence by ultraviolet irradiation.