THE SNAP45 SUBUNIT OF THE SMALL NUCLEAR-RNA (SNRNA) ACTIVATING PROTEIN COMPLEX IS REQUIRED FOR RNA-POLYMERASE-II AND RNA-POLYMERASE-III SNRNA GENE-TRANSCRIPTION AND INTERACTS WITH THE TATA BOX-BINDING PROTEIN
Cl. Sadowski et al., THE SNAP45 SUBUNIT OF THE SMALL NUCLEAR-RNA (SNRNA) ACTIVATING PROTEIN COMPLEX IS REQUIRED FOR RNA-POLYMERASE-II AND RNA-POLYMERASE-III SNRNA GENE-TRANSCRIPTION AND INTERACTS WITH THE TATA BOX-BINDING PROTEIN, Proceedings of the National Academy of Sciences of the United Statesof America, 93(9), 1996, pp. 4289-4293
The RNA polymerase II and III small nuclear RNA (snRNA) promoters cont
ain a common basal promoter element, the proximal sequence element (PS
E). The PSE binds a multisubunit complex we refer to as the snRNA acti
vating protein complex (SNAP(c)). At least four polypeptides are visib
le in purified SNAP(c) preparations, which migrate with apparent molec
ular masses of 43, 45, 50, and 190 kDa on SDS/polyacrylamide gels. In
addition, purified preparations of SNAP(c) contain variable amounts of
TATA box binding protein (TBP). An important question is whether the
PSEs of RNA polymerase II and III snRNA promoters recruit the exact sa
me SNAP(c) complex or slightly different versions of SNAP(c), differin
g, for example, by the presence or absence of a subunit. To address th
is question, we are isolating cDNAs encoding different subunits of SNA
P(c). We have previously isolated the cDNA encoding the 43-kDa subunit
SNAP43. We now report the isolation of the cDNA that encodes the p45
polypeptide. Antibodies directed against p45 retard the mobility of th
e SNAP(c)-PSE complex in an electrophoretic mobility shift assay, indi
cating that p45 is indeed part of SNAP(c). We therefore refer to this
protein as SNAP45. SNAP45 is exceptionally proline-rich, interacts str
ongly with TBP, and, like SNAP43, is required for both RNA polymerase
II and III transcription of snRNA genes.