Association of a polyuridylate‐specific endoribonuclease with small nuclear ribonucleo‐proteins which had been isolated by affinity chromatography using antibodies from a patient with systemic lupus erythematosus

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Abstract
Ig, containing antibodies against U1-snRNP [small nuclear ribonucleoprotein], were prepared from a patient with systemic lupus erythematosus. After coupling these antibodies to a Sepharose matrix. U-snRNP were isolated and purified from rat liver nuclei by use of immunoaffinity chromatography. The resulting RNP had the typical protein pattern of U-snRNP and a sedimentation coefficient of 12 S. The U-snRNP preparation was associated with an endoRNase which required Mg2+ for optimal activity. The enzyme, with an pH optimum of 6.2, degraded only poly(U). Other single-stranded polyribo- and polydeoxyribonucleotides, tRNA, as well as double-stranded RNA and DNA were not digested. The products of a terminal digestion are (U)6-12 with 3''-OH and 5''-P termini. The possible involvement of this endoRNase in the in the splicing of hn[heterogenous nuclear]RNA is discussed.