AUG is not the only inititation codon. GUG, UUG and even CUG can be used as the inititation codon, and that is only looking at the standard code.

Same with Trp. Yes, there is a single codon for Trp in the standard code, but there are plenty of exceptions (in mitochondriae from many kingdoms UGA codes for Trp as well, for instance).

I have been working on this point for a while and that is why i came to this question which really first is a copy of a question from Chemistry Forum dated on 2010!!!. I really was puzzling about that and my working hypothesis that there is a role for tryptophan in protein translation control yet to be discovered as a simple explanation. Yes there are several exceptions for standard genetic code but over the billion of years of evolution there is only one codon as methionine code for tryptophan, so there must be a missing role need to be shown.

Ask yourself what do codons and ubiquitin marking have in common? The answer is circadian biology. When the circadina mechanism is disrupted protein synthesis is increased and often not yoked to proper solar signals. Since we know melanopsin is now present in eye, skin, and dermal fat it is becoming clear ubiquitin is linked to the melanopsin system. That opsin is linked, via sunlight to cytochrome 1, NADH/NAD+ couple. Tryptophan has a unique absorption spectrum that hints it is a seasonal time crystal and it can be used by the endogenous timing mechanism by the addition of information and energy from photons, electrons, or by protons. These two aspects of subatomic particles program typtophan differently in seasons because season have a different electromagnetic foot print codified by photosynthesis in food and this is decipered by mitochondria. This is why Tryptophan can be both ketogenic and glucogenic depending on how it was created by the sun. Methionine is the exogenous time crystal because it is also unique with one codon. It is an essential amino acid therefore, it give energy and information to the mitochondria from the environment the animal is inhabiting. That signal must be yoked to the incoming light signals via the eye and skin. The mt DNA deciphers the message to pass it on to the nucleus to change epigenetic signaling via the addition or subtration of electrons, protons and photons to histones and methyl groups to affect chromatin binding and DNA kinetics and the Auger effect in cells.

damn Dr. Kruse, you on top of it Lol took me forever to catch up