Autoantigenic epitopes of the B polypeptide of Sm small nuclear RNP particles. Identification of regions accessible only within the U1 small nuclear RNP.
OBJECTIVE
To analyze the autoantigenic epitopes of the Sm B polypeptide of the U1 small nuclear RNP (snRNP) using complementary DNA (cDNA) clones.


METHODS
Expression of Sm B fusion proteins in lambda phage vectors, immunoblots, immunoprecipitations, and affinity purification of antibodies.


RESULTS
Immunoblots using antibodies affinity-purified from B fusion proteins demonstrated that there were cross-reactive epitopes between the B'/B and A polypeptides of the U1 snRNP. Immunoprecipitation assays suggested that there were at least 3 different autoantigenic epitopes on the B polypeptide that could be classified into 2 general groups based upon autoantibody reactivity. The first group of autoantibodies, which bound 2 separate autoantigenic epitopes (BU1-1, BU1-2), participated in immunoprecipitation of the U1 snRNP alone. The second group, which bound the third type of autoantigenic epitope (BSm-1), immunoprecipitated all the abundant Sm snRNPs.


CONCLUSIONS
There is at least 1 region on the B proteins that is accessible to antibodies only within the structure of the U1 snRNP, as well as a region that is accessible on all Sm snRNPs. These data support the notion that the native U1 RNP, perhaps containing B proteins in a different conformation than those found on other Sm snRNPs, may drive the humoral immune response in systemic lupus erythematosus.
Ohosone
Y
Y
Department of Internal Medicine, Kawasaki Municipal Hospital, Kanagawa, Japan.
Mimori
T
T
Fujii
T
T
Akizuki
M
M
Matsuoka
Y
Y
Irimajiri
S
S
Hardin
J A
JA
Craft
J
J
Homma
M
M
D000595:Amino Acid Sequence; D001324:Autoantigens / Q000235:genetics / Q000276:immunology*; D004247:DNA / Q000032:analysis / Q000235:genetics; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D006801:Humans; D015151:Immunoblotting; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000276:immunology*; D011233:Precipitin Tests; D012261:Ribonucleoproteins / Q000235:genetics / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear
D001324:Autoantigens; D000939:Epitopes; D010455:Peptides; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D004247:DNA