Determining a protein’s primary structure by DNA sequencing

The sequence of nucleotides in a protein-coding region of the DNA specifies the amino acid sequence of a polypeptide. Therefore, if the nucleotide sequence can be determined, knowledge of the genetic code  allows the sequence of nucleotides to be translated into the corresponding amino acid sequence of that polypeptide. This indirect
process, although routinely used to obtain the amino acid sequences of proteins, has the limitations of not being able to predict the positions of disulfide bonds in the folded chain and of not identifying any amino acids that are modified after their incorporation into the polypeptide (posttranslational modification). Therefore, direct protein sequencing is an extremely important tool for determining the true character of the primary sequence of many polypeptides.