Immature oocytes from Xenopus Iaevls contain a 42S ribonucleoprotein particle (RNP) containing 5S RNA, tRNA, a 43 kDa protein, and a 48 kDa protein. A particle containing 5S RNA and the 43 kDa protein (p43-5S) liberated from the 42S particle upon brief treatment with urea can be purified by anion exchange chromatography. The purified p43-5S RNA migrates as a distinct species during eiectrophoresis on native potyacryiamide gels. Radiolabeled 5S RNA can be incorporated into the p43-5S complex by an RNA exchange reaction. The resulting complexes containing labeled 5S RNA have a mobility on potyacryiamide gels identical to that of purified p43-5S RNPs. RNP complexes containing 5S RNA labeled at either the 5′ or 3′ end were probed with a variety of nucleases in order to identify residues protected by p43. Nuclease protection assays performed with α-sarcin indicate that p43 binds primarily helices I, II, IV, and V of 5S RNA. This Is the same general binding site observed for TFIIIA on 5S RNA. Direct comparison of the binding sites of p43 aand TFIIIA with T1 and cobra venom nucleases reveals striking differences in the protection patterns of these two proteins.

Original languageEnglish
Pages (from-to)1797-1803
Number of pages7
JournalNucleic acids research
Issue number8
StatePublished - Apr 25 1991


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