cDNA sequence of the rat U snRNP-associated protein N: description of a potential Sm epitope.
Anti-Sm antibodies from a patient with systemic lupus erythematosus (SLE) were used to isolate cDNA clones encoding the snRNP-associated protein N from a rat brain derived cDNA library. The predicted primary structure of the 240 amino acid protein has a proline rich carboxyl terminus and shares a region of sequence similarity with other snRNP polypeptides, A and B/B'. Anti-Sm sera recognize a beta-galactosidase fusion protein containing only the carboxyl-terminal 80 amino acids of N; antibodies eluted from this fusion protein also react with A, B/B' and N on immunoblots, suggesting that these proteins share an Sm epitope located within this segment. Polyclonal antibodies raised against a 23 amino acid synthetic peptide derived from this conserved region of N recognize A, N and B/B' on immunoblots and can immunoprecipitate the Sm class of U snRNAs. These results confirm that this sequence defines a potential Sm epitope. RNA blotting analyses demonstrate that a 1.6 kb mRNA expressed predominantly in brain encodes the N polypeptide in both rats and humans. At low stringency rat N cDNA also hybridizes to a 1.3 kb mRNA species which encodes B/B', suggesting that N is structurally related to, but distinct from B/B'. Although B/B' proteins are thought to be expressed in all human cells, only N and B, but not B', are observed on immunoblots of human brain proteins probed with anti-Sm sera. The apparent difference in the complement of proteins associated with snRNP particles in human brain versus elsewhere suggests a possible mechanism for the regulation of brain-specific mRNA splicing.
McAllister
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G
Section of Molecular Neurobiology, Howard Hughes Medical Institute Research Laboratories, Yale University School of Medicine, New Haven, CT 06510.
Roby-Shemkovitz
A
A
Amara
S G
SG
Lerner
M R
MR
D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000235:genetics*; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D051381:Rats; D012261:Ribonucleoproteins / Q000235:genetics*; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins
D001324:Autoantigens; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins; D004247:DNA