Which statement accurately defines an intron?

An intron is accurately defined as a non-coding sequence that is present within a gene and is removed from the precursor mRNA (pre-mRNA) during the process of RNA splicing. When a gene is transcribed, both coding sequences (exons) and non-coding sequences (introns) are initially included in the pre-mRNA. However, before the mature mRNA is translated into a protein, the introns are excised, and the exons are joined together. This removal is essential for producing a functional mRNA that codes for a protein.

The significance of introns lies in their potential roles in gene expression regulation and alternative splicing, allowing for the production of multiple protein variants from a single gene. This contributes to the complexity and diversity of proteins that can be synthesized in an organism.

The other definitions do not accurately describe introns. A coding sequence refers to exons that are translated into proteins, while sequences that initiate transcription are typically promoters found upstream of the coding region. Regulatory proteins do not describe any part of the DNA itself but rather the proteins involved in controlling gene expression.