Which DNA strand can serve as a template for RNA synthesis?

Both strands of DNA can serve as templates for RNA synthesis, depending on the context of transcription. The positive strand, also known as the coding or sense strand, has the same sequence as the RNA transcript (with thymine replaced by uracil). This strand is often referred to in discussions of genetic coding because it contains the information that is ultimately reflected in the protein products.

On the other hand, the negative strand, or template strand, is complementary to the positive strand and is used as the actual template during the process of transcription. RNA polymerase binds to the template strand and synthesizes RNA in a 5' to 3' direction, following the base-pairing rules: adenine (A) in DNA pairs with uracil (U) in RNA, and cytosine (C) pairs with guanine (G).

In many organisms, particularly in eukaryotes, transcription involves both strands. Some genes may be transcribed from the positive strand, while others can be transcribed from the negative strand. Thus, the ability of both the positive and negative strands to serve as templates for RNA synthesis justifies the assertion that both strands are necessary in terms of genetic diversity and expression regulation in various cellular conditions.