Synthesis of ribosomal proteins L7L12 in relaxed and stringent strains of Escherichia coli.
The control of the synthesis of ribosomal proteins L7L12 (which lack histidine) was examined during growth and histidine starvation of stringent and relaxed histidine mutants. Since no ribosomes are synthesized during starvation, these proteins, in both the stringent and relaxed organisms, accumulated in the supernatant and were shown to possess both biological and physical characteristics typical of normal L7L12. However, the rate and extent of synthesis of these proteins during starvation is greater in the relaxed strain than in the stringent. These data suggest that the regulation of the synthesis of these proteins, similar to that of ribosomal RNA is regulated by the stringent control system. It was also shown that during normal growth of both organisms, L7L12 is also found in the supernatant as well as on the ribosomes. The L7L12 found in the supernatant under these conditions, however, appears to be different than ribosomal L7L12.