KINETICS OF MATURATION OF AMINO TERMINI OF CELL PROTEINS OF ESCHERICHIA COLI

1. 1. The removal of the initiating N-formylmethionine termini of Escherichia coli cell protein has been followed with [14C]methionine labeling during biosynthesis under a variety of conditions. Label equilibrates first into internal protein linkages, and then into both free and masked N-termini. The masking group has the acid lability of N-formylmethionine. 2. 2. Some deformylation is immediate or lagless, as can be demonstrated with ribosomal protein in the presence of chloramphenicol. 3. 3. In one-third or more of the cell protein deformylation requires about the time (5 sec) needed for polypeptide assembly during growth. The interval is unaffected by uracil depletion but increases to 10-20 sec during starvation of one or more amino acids and even longer with the RCrel mutant. From the findings with uracil depletion, the translation time of an average cell protein appears relatively uninfluenced by the presence or absence of growth per se. 4. 4. Many N-termini of cell proteins are stably formylated, and can be isolated intact from cell protein more than a generation after synthesis. 5. 5. Loss of initiating methionine, as judged from the unmasking of subterminal [14C]alanine is comparatively sluggish, requiring a minimum of 8 sec and an average of 36 sec in growth. © 1969.