Metabolism of ribosomes during thiamine starvation and restoration in Lactobacillus viridescens

Abstract

1. Thiamine starvation of the thiamine auxotroph Lactabacillus viridescens causes partial degradation of ribosomes. The remaining ribosomes are inactive but dissociate into 30-S and 50-S subunits. 2. Two-dimensional electrophoresis of ribosomal proteins from starved cells revealed: two proteins, occurring in 70-S ribosomal fractions from exponential grown cells, with electrophoretic mobilities close to S 1 and L 3, are missing; one additional protein is found in the region of L 7; several ribosomal proteins show in repeated experiments increased electrophoretic mobility. 3. 1–2 h upon thiamine restoration the cells do not divide. During this time radioactive amino acids are incorporated into ribosomal proteins, predominantly into the proteins of the large subunit, especially into L 14. Furthermore [ 3H]uridine is incorporated preferentially into ribosomal RNAs, 16-S and 23-S rRNA become labelled at a ratio of 1:1. 4. Ribosomal fractions from thiamine-restored cells sediment faster in sucrose gradients, at 10 −4 M Mg 2+, than 30-S and 50-S subunits; their ability to function in the cell-free system of polyphenylalanine synthesis is partially restored. These results suggest that, during the early phase of recovery, the cells contain a mixture of old, newly formed ribosomes and ribosomal precursors.