scholarly journals Molecular cloning of cDNA encoding Sm autoantigen: Derivation of a cDNA for a B polypeptide of the U series of small nuclear ribonucleoprotein particles

1989 ◽  
Vol 86 (22) ◽  
pp. 8982-8982
Keyword(s):  
Molecular Cloning ◽  
Small Nuclear Ribonucleoprotein ◽  
Ribonucleoprotein Particles ◽  
Nuclear Ribonucleoprotein

scholarly journals Molecular Characterization of a Novel, Widespread Nuclear Protein That Colocalizes with Spliceosome Components

1998 ◽  
Vol 9 (1) ◽  
pp. 143-160 ◽  
Author(s):  
Marion S. Schmidt-Zachmann ◽  
Sylvia Knecht ◽  
Angela Krämer
Keyword(s):  
Molecular Characterization ◽  
Nuclear Protein ◽  
Cultured Cells ◽  
Splicing Factors ◽  
Nuclear Speckles ◽  
Sm Proteins ◽  
Small Nuclear Ribonucleoprotein ◽  
Ribonucleoprotein Particles ◽  
Nuclear Ribonucleoprotein

We report the identification and molecular characterization of a novel type of constitutive nuclear protein that is present in diverse vertebrate species, from Xenopus laevis to human. The cDNA-deduced amino acid sequence of the Xenopus protein defines a polypeptide of a calculated mass of 146.2 kDa and a isoelectric point of 6.8, with a conspicuous domain enriched in the dipeptide TP (threonine-proline) near its amino terminus. Immunolocalization studies in cultured cells and tissues sections of different origin revealed an exclusive nuclear localization of the protein. The protein is diffusely distributed in the nucleoplasm but concentrated in nuclear speckles, which represent a subnuclear compartment enriched in small nuclear ribonucleoprotein particles and other splicing factors, as confirmed by colocalization with certain splicing factors and Sm proteins. During mitosis, when transcription and splicing are downregulated, the protein is released from the nuclear speckles and transiently dispersed throughout the cytoplasm. Biochemical experiments have shown that the protein is recovered in a ∼12S complex, and gel filtration studies confirm that the protein is part of a large particle. Immunoprecipitation and Western blot analysis of chromatographic fractions enriched in human U2 small nuclear ribonucleoprotein particles of distinct sizes (12S, 15S, and 17S), reflecting their variable association with splicing factors SF3a and SF3b, strongly suggests that the 146-kDa protein reported here is a constituent of the SF3b complex.

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