Wheat-embryo ribonucleates. IV. Factors that influence the formation and stability of a complex between 5S rRNA and 18S rRNA.

Under the conditions used in this study, wheat-embryo 5S rRNA complexes with its homologous 18S rRNA from wheat embryos and with heterologous 18S rRNA from other eukaryotic source materials such as yeast, L cells, and HeLa cells, but it does not complex with heterologous 16S rRNA from a prokaryote such as Escherichia coli or with homologous or heterologous 26S (23S) rRNA of either eukaryotic or prokaryotic origin. If a solution of wheat-embryo rRNA is simply made 0.3 M with respect to NaCl and then heated at 60 degress C for 3 min before quick cooling to room temperature (ca. 20 degrees C), there is both preferential and efficient complex formation between 5S and 18S rRNA. The 'laboratory-prepared' complex between wheat-embryo 5S rRNA and its homologous 18S rRNA is more thermostable in 0.1 M NaCl solution than is the 'natural' complexes 'melt' over a narrow range of temperature. The possible physicochemical and physiological importance of both homologous and heterologous rRNA complexes is the subject of a brief discussion.