Refer figure 9-3 (c):
Changing from sense to nonsense codons, the stop codons UAG (amber), UAA (ochre) or UGA (opal) may lead to the termination of polypeptide chain resulting in total loss of gene function. The nonsense suppressors are the mutations in genes encoding tRNAs (transfer ribonucleic acid), which are called tRNA suppressors, which changes the anticodon loops of particular tRNA in such a way that a tRNA develop to identify a stop codon in mRNA (messenger ribonucleic acid).
The three-dimensional structure of a single protein molecule leads to tertiary structure. The formation of compact globule, the α-helices and β-sheets are folded by the formation of non-specific hydrophobic interactions and disulfide bonds. Correct folding is based on the amino acid sequence that is essential for proper protein function.
The exact tertiary structure could not form due to the replacement of an amino acid that causes a loss of function for the protein by disturbing the folding of the β-subunit. If a later mutation in one more regions of β-subunit set off the first mutation, through moderately bring back the normal folding model, acceptable tertiary structure could form and the first mutation will probably suppressed.