Small-Size mRNAs Code for Ribosomal Proteins in Yeast

Abstract

To identify and to study the ribosomal protein genes in yeast an attempt was made to purify the mRNA coding for ribosomal proteins. Poly(A)-containing RNA from the yeast S. carlsbergensis was fractionated according to size using preparative sucrose gradient centrifugation. The various (size) fractions were translated in vitro in a wheat germ cell-free system. The products were analyzed by sodium dodecyl sulfate/polyacrylamide gradient gel electrophoresis as well as by acetic acid/urea gel electrophoresis. An mRNA fraction of about 9S directs the synthesis in vitro of proteins that have properties characteristic of ribosomal proteins, i.e., they are both small and basic. The ribosomal nature of these proteins was further established by 2-dimensional gel electrophoresis. This small-size mRNA fraction can be used as a probe for the identification of ribosomal protein genes in recombinant DNA molecules.