Abstract
The snRNP particles include a set of common core snRNP proteins and snRNP specific proteins. In rodent cells the common core proteins are the B, D, D', E, F and G proteins in a suggested stoichiometry of B2D'2D2EFG. The additional U1- and U2-specific proteins are the 70-kD, A and C proteins and the A' and B" proteins, respectively. Previous cell fractionation and kinetic analysis demonstrated the snRNP core proteins are stored in the cytoplasm in large partially assembled snRNA-free intermediates that assemble with newly synthesized snRNAs during their transient appearance in the cytoplasm (Sauterer, R. A., R. J. Feeney, and G. W. Zieve. 1988. Exp. Cell Res. 176:344-359). This report investigates the assembly and intracellular distribution of the U1 and U2 snRNP-specific proteins. Cell enucleation and aqueous cell fractionation are used to prepare nuclear and cytoplasmic fractions and the U1- and U2-specific proteins are identified by isotopic labeling and immunoprecipitation or by immunoblotting with specific autoimmune antisera. The A, C, and A' proteins are found both assembled into mature nuclear snRNP particles and in unassembled pools in the nucleus that exchange with the assembled snRNP particles. The unassembled proteins leak from isolated nuclei prepared by detergent extraction. The unassembled A' protein sediments at 4S-6S in structures that may be multimers. The 70-kD and B" proteins are fully assembled with snRNP particles which do not leak from isolated nuclei. The kinetic studies suggest that the B" protein assembles with the U2 particle in the cytoplasm before it enters the nucleus.
Highlights
The snRNP particles include a set of common core snRNP proteins and snRNP specific proteins
Abbreviations used in this paper: NLS, nuclear localization signal; SLE, systemic lupus erythromatosus~ suspension culture in minimal essential medium (SMEM), suspension minimal essential medium
In addition to the snRNP core proteins shared by all the nucleoplasmic snRNP particles, there are snRNP-specific proteins
Summary
The snRNP particles include a set of common core snRNP proteins and snRNP specific proteins. The common core of snRNP protein in rodent cells consists of the B, D, D', E, F and G proteins in a suggested stoichiometry of B2D'2D2EFG. (For review see Brunel et al, 1985; Reddy and Busch, 1988; Zieve and Sauterer, 1990.) Autoimmune antisera from patients with systemic lupus erythematosus SnRNP core assembly is directed by a conserved sequence motif of PuA(U)nGPu (n > 3) present in a single stranded region of the snRNA (for review see Parry, 1988; Zieve and Feeney, 1989). Abbreviations used in this paper: NLS, nuclear localization signal; SLE, systemic lupus erythromatosus~ SMEM, suspension minimal essential medium
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