Messenger RNA for ribosomal proteins in Xenopus laevis oocytes.

Xenopus laevis oocytes (stage II--III) incorporate [35S]methionine into ribosomal proteins identifiable by two-dimensional electrophoresis. Poly(A)-rich RNA prepared form this source has been translated in a wheat germ cell-free system. Among the products synthesized in vitro 30 are clearly identifiable as ribosomal proteins. Some are not individually resolved, whereas a few of them may lack methionine or may not be correctly processed after the synthesis in vitro. An enrichment of our mRNA preparation for ribosomal protein activity can be obtained by subsequent passages on oligo(dT)-cellulose columns and by selection of a 10--16-S fraction by sucrose gradient sedimentation. We estimate that messenger RNA for ribosomal proteins represents 10--20% of this RNA preparation and can now be utilized for molecular cloning procedures.