New Roles for Amino Acid Codons
Here is a short evaluation I wrote for f1000. It briefs a recent paper in Science titled “Differential arginylation of actin isoforms is regulated by coding sequence-dependent degradation” by Zhang et al.
Although the discovery that there are multiple codons for each amino acid was made decades ago, still little is known about whether those extra codons are redundant or not. Because the AT content of genomic DNA varies widely from 30-70% on the coding regions across species (see ref {1}, on which Jike Cui is an author), codons fitting the background AT content could probably be favored. While that is a reasonable hypothesis for the different usages of codons coding for the same amino acid, recent reports and reviews shed much brighter light on this topic {2,3}.
Mammalian cytoskeletal proteins beta- and gamma-actin share 98% amino acid identity; however, they have very distinct roles in cells. The reason is that beta-actin is arginylated, whereas gamma-actin is not. The question is that, if the 2% difference in amino acid sequence cannot explain why one undergoes the post-translational modification and the other does not, then what does? Here, Zhang et al. found that identical amino acid segments between the two actins have different codons, which leads to a different speed of translation and that the different speed results in the distinction in arginylation.
This discovery provides a new angle to study the mechanisms of co- and post-translational modification, and it will also have an impact on understanding gene evolution.
References: {1} Cui et al. Proc Natl Acad Sci USA 2009, 106:13421-6 [PMID:19666543]. {2} Weygand-Durasevic and Ibba, Science 2010, 329:1473-4 [PMID:20847254]. {3} Baker M, Nat Methods 2010, 7:874 [PMID:21049579].