Biosynthesis of 50 s ribosomal subunit in Escherichia coli

Abstract

Two intermediate particles of 50 s ribosome formation, i.e. [30 s]- and 40 s nascent or precursor particles, were isolated from exponentially growing Escherichia coli cells. Particles indistinguishable from these nascent ribosomal particles were found in the extracts of the cells treated with a low concentration of chloramphenicol. The [30 s]-particles contain undermethylated 23 s rRNA and three main protein components. The 40 s particles also possess undermethylated 23 s rRNA and, in addition to the three protein components found in the [30 s]-particles, 9 other components out of 19 components detectable in the 50 s ribosomal subunit. Both particles include little 5 s RNA. Based on the above findings, a scheme for the biosynthesis of 50 s ribosomal subunits is presented. The protein compositions and 5 s RNA contents of the nascent ribosomal particles are compared with those of protein-deficient particles obtained by exposing 50 s ribosomal subunits to a concentrated LiCl solution. The molecular compositions of these two kinds of particles are found to be similar, but not exactly the same.