Fine Structure of Snrnps

Abstract Core snRNPs isolated under very drastic conditions contain the same subset of a few small proteins, including an Sm antigen recognized by systemic lupus erythematosus (SLE) patients, bound to an evolutionary conserved domain common to all but U6 snRNAs. This domain consists of a single stranded region comprising the sequence A(U)nG bordered by two double-stranded stems. We have now extended this analysis to snRNPs purified in a more native configuration. In U1 snRNP which is now recognized by both anti-RNP and anti-Sm SLE sera, we found that the entire U1 snRNA sequence is protected except for the ten 5′ terminal nucleotides involved in splicing. In U2 snRNP, the 5′ two-thirds of U2 snRNA remain exposed while the 3′ hairpin located outside the core structure becomes protected. In U5 and U4-U6 snRNPs the protected fragment is a mere extension of the core resistant structure.