Wheat embryo ribonucleates. VII. Rapid, efficient and selective formation of 5S-18S and 5.8S-26S hybrids in an aqueous solution of the four ribosomal polynucleotides, and the results of a search for the corresponding hybrids in wheat embryo ribosomes.

(1) If wheat embryo 5S and 5.8S rRNA are differentially labelled, it can be shown that there is highly selective association of 5S [14C]RNA with 18S rRNA, and of 5.8S [3H]RNA with 26S rRNA when a solution (0.3 M NaCl) that contains approximately equimolar amounts of the four ribosomal polynucleotides is heated briefly (3 min) at 60 degrees C. (2) Comparison of Tm values and melting profiles for laboratory-prepared and natural 5.8S-26S rRNA hybrids suggests that restoration of the natural union between 5.8S and 26 rRNA can be achieved with facility and fidelity in the laboratory. (3) Union between 5.8S rRNA remains intact when wheat embryo ribosomes are disintegrated either by digestion with pronase or by treatment with sodium dodecyl sulphate, but the same treatments release 5S and 18S rRNA as freely migrating electrophoretic components. (4) Intact 18S and 26S rRNA can be prepared from small and large subunits, respectively, when wheat embryo ribosomes are dissociated by treatment with 0.5 M KCl. (5) Incidental to the principal investigation, it has been shown that, even after storage for more than 6 years at -70 degrees C, commercial supplies of roller-milled wheat germ yield S23 extracts that are very active in the cell-free translation of globin mRNA. (6) The physicochemical and possible biochemical significance of various types of intermolecular complexing between pairs of ribosomal polynucleotides is a subject of discussion.