Two eukaryotic proteins are identical except for one domain in each protein, and these two domains are completely different from each other. Which of the following processes is most likely to have contributed to this difference?

Alternative splicing.

Explanation:

The eukaryotes translation process requires two more step known as polyadenylation and capping. The transcription and translation occurs in the separate compartment.

The eukaryotes genome consists of both the exons as well as introns. The introns need to be excise out and exons join together in the process known as alternative splicing. This alternative splicing is responsible for the formation of the different protein.

Thus, the answer is alternative splicing.