Question

Review the concept of colinearity and consider the following question: Certain mutations called amber in bacteria and viruses result in premature termination of polypeptide chains during translation. Many amber mutations have been detected at different points along the gene that codes for a head protein in phage T4. How might this system be further investigated to demonstrate and support the concept of colinearity?

Accepted Answer

Step 1: Understand the concept of colinearity, which states that the sequence of nucleotides in a gene corresponds directly and linearly to the sequence of amino acids in the protein it encodes. This means that mutations at different points in the gene should affect the protein at corresponding positions. Step 2: Recognize that amber mutations cause premature stop codons, leading to truncated proteins. By identifying the exact location of these mutations within the gene, you can predict where the protein synthesis stops. Step 3: Map the positions of the amber mutations along the DNA sequence of the gene and correlate these positions with the lengths of the truncated polypeptides produced. This can be done by analyzing the size of the protein fragments using techniques such as SDS-PAGE. Step 4: Demonstrate that mutations occurring earlier in the gene produce shorter polypeptides, while mutations occurring later produce longer polypeptides. This linear relationship supports the idea of colinearity between the gene and its protein product. Step 5: To further support colinearity, complement genetic data with molecular techniques such as sequencing the mutated gene regions and comparing the mutation sites with the corresponding truncated protein products, confirming the direct correspondence between gene sequence and protein structure.

Key Concepts

Colinearity of Genes and Proteins

Amber Mutations and Nonsense Codons

Use of Phage T4 as a Model System