Skip to main content
. 2021 Aug 13;118(33):e2107829118. doi: 10.1073/pnas.2107829118

Fig. 4.

Fig. 4.

tRNA and aa-tRNA-synt. (aaS) autocatalytic cycles and growth laws. (A) The tRNA autocatalytic cycle. tRNAs are transcribed by RNA polymerases (poly.). After the maturation process (not shown), each tRNA is charged with an amino acid and loaded onto EF-Tu. The EF-Tu-tRNA-aa is also charged with GTP (not shown) and subsequently delivers the amino acid to the ribosome. This cycle repeats until the tRNA degrades in a time scale that we assume to be much longer than the doubling time. Some of the delivered amino acids are embedded in Rpo proteins, which self-assemble to form new RNA polymerases, some of which are allocated to transcribe tRNAs, thus completing the cycle. (B) The aa-tRNA-synt. autocatalytic cycle. An aa-tRNA-synt. protein of a specified type charges tRNA with its corresponding amino acid. A fraction of the charged tRNAs contributes the amino acids to form new aa-tRNA-synt. of the same type, thus completing the cycle. In the middle of the figure, we show the ratio between tRNA of type i and its associated aa-tRNA-synt. Neglecting cross-charging, this ratio equals, at balanced growth, the ratio of the charging cycle duration to the charging duration.