Which of the following is NOT a step in eukaryotic mRNA processing?

The process of eukaryotic mRNA processing involves several crucial steps that occur between transcription and translation. The addition of a 5' cap is important for protecting the mRNA from degradation and assists in ribosome recognition during translation. The poly(A) tail added at the 3' end serves similar protective functions and helps in the regulation of mRNA stability and transport out of the nucleus. RNA splicing is essential for removing non-coding sequences (introns) from the pre-mRNA, which results in the formation of a mature mRNA that can be translated into a protein.

In contrast, replicating DNA is not a part of mRNA processing. DNA replication occurs during the S phase of the cell cycle, preceding transcription, which is the step where mRNA is synthesized from DNA. Since replication pertains to duplicating the genetic material of the cell, it is distinct from the processing of mRNA that happens after transcription. Therefore, this choice accurately identifies a process that is not included in eukaryotic mRNA processing.