One of the following is true with respect to AUG:

Options

A. It codes for methionine only
B. It is also an initiation codon
C. It codes for methionine in both prokaryotes and eukaryotes
D. All of the above

Answer

To solve the question regarding the codon AUG, we will analyze each of the provided statements step by step to determine which one is true.

### Step 1: Understand what AUG represents
AUG is a codon that is important in the genetic code. It is known as the start codon and is responsible for initiating protein synthesis.

**Hint:** Remember that codons are sequences of three nucleotides that correspond to specific amino acids or signals during protein synthesis.

### Step 2: Evaluate the first statement
The first statement claims that AUG codes for methionine only. This statement is partially correct because AUG does indeed code for methionine, but it is important to note that in prokaryotes, it codes for a modified form called N-formylmethionine (fMet).

**Hint:** Consider the context of the organism when evaluating what a codon codes for.

### Step 3: Evaluate the second statement
The second statement indicates that AUG is also an initiation codon. This statement is true, as AUG serves as the start codon for protein synthesis in both eukaryotes and archaebacteria. In prokaryotes, it codes for formylated methionine.

**Hint:** Think about the role of AUG in the initiation of translation.

### Step 4: Evaluate the third statement
The third statement asserts that AUG codes for methionine in both prokaryotes and eukaryotes. This is misleading because while AUG does code for methionine in eukaryotes, in prokaryotes, it codes for formylated methionine (fMet).

**Hint:** Pay attention to the specifics of what each organism uses.

### Step 5: Evaluate the fourth statement
The fourth statement claims that all of the above statements are correct. Since the first and third statements contain inaccuracies, this statement cannot be true.

**Hint:** If one of the statements is incorrect, then "all of the above" cannot be true.

### Conclusion
The correct statement regarding AUG is that it is an initiation codon that codes for methionine in eukaryotes and archaebacteria, and for formylated methionine in prokaryotes. Therefore, the correct choice would be the second statement.

### Final Answer
The correct statement with respect to AUG is: "It is also an initiation codon."