Purification of two thermostable components of messenger ribonucleoprotein particles (mRNPs) from <i>Xenopus laevis</i> oocytes, belonging to a novel class of RNA‐binding proteins

Abstract

We have purified and partially sequenced two proteins from Xenopus laevis previtellogenic oocytes, belonging to messenger ribonucleoprotein particles (mRNPs). The purification procedure rests on the thermostability of these proteins, which remain soluble after heating the cell extracts at 80 degrees C. The thermostable proteins can be identified with two of the most abundant components (mRNP3 and mRNP4) of the mRNPs, described by Darnbrough and Ford (1981) [Eur. J. Biochem. 118, 415-424]. mRNP3 and mRNP4 are homologous to each other, but to no other protein of known sequence. The abundance and semi-periodic distribution of proline residues in mRNP3 and mRNP4 sequences suggest that these RNA-binding proteins adopt an unusual type of conformation.