Which enzyme is responsible for copying a DNA sequence into an RNA sequence?

The enzyme responsible for copying a DNA sequence into an RNA sequence is RNA polymerase. This enzyme plays a crucial role during the process of transcription, where it binds to the DNA template strand and synthesizes a complementary RNA strand. RNA polymerase utilizes the base-pairing rules: adenine in the DNA pairs with uracil in RNA, and cytosine pairs with guanine. This conversion from DNA to RNA is essential for gene expression, as the resultant RNA serves as a template for protein synthesis during translation.

In contrast, DNA polymerase is primarily involved in DNA replication, where it synthesizes new DNA strands complementary to existing DNA templates. Ligase is responsible for joining Okazaki fragments on the lagging strand during DNA replication, and helicase unwinds the DNA double helix, allowing access for the replication and transcription machinery. Thus, RNA polymerase is the correct choice for the enzyme that specifically performs the task of transcribing DNA into RNA.