Alteration in the Acetylation Level of Ribosomal Protein L12 during Growth Cycle of Escherichia coli

The relative content in ribosomes of L7 and L12, the two forms of a protein in the 50S subunit specifically involved in GTP hydrolysis, is found to undergo a striking shift with the growth phase of E. coli. The content of L12 (nonacetylated form) increases during early logarithmic phase, becoming about 85% of the total before midlogarithmic phase. Thereafter, L7 (N-acetylated form) content begins to increase, eventually becoming 75-80% in stationary phase. The L7 + L12 content per ribosome, however, remained constant during this shift. Our evidence suggests that the shift did not occur through modification of preexisting ribosomes. The data further indicate that the E. coli cell may contain more than one structurally distinct (with regard to L7 or L12 content) 50S subunit population.