Question

The presence of a DNA template (e.g., a product from PCR), general transcription factors, and RNA polymerase II allows for the initiation of transcription in vitro. Explain why the initiation of transcription is not possible with only general transcription factors and RNA polymerase II using the genomic DNA as a template.

(a) Genomic DNA is wrapped in nucleosomes, while template DNA from PCR is not. For remodeling or removing nucleosomes additional proteins are required.
(b) Template DNA from PCR is wrapped in nucleosomes, while genomic DNA is not.
(c) The nucleosomes are required for initiation of transcription.
(d) None of the above.

Answer 1

The initiation of transcription in vitro with genomic DNA as a template is not possible without additional proteins to remodel or remove nucleosomes, whereas PCR product DNA doesn't have nucleosomes, allowing easy access for transcription factors and RNA polymerase.

Step-by-step explanation:

The initiation of transcription in vitro requires a DNA template in addition to general transcription factors and RNA polymerase II. The answer to the student's question is (a) Genomic DNA is wrapped in nucleosomes, while template DNA from PCR is not. For remodeling or removing nucleosomes, additional proteins are required. During in vivo transcription, the genomic DNA is organized into chromatin and is tightly associated with histone proteins to form nucleosomes, which presents a barrier to the transcription machinery. For transcription to occur, these nucleosomes need to be remodeled or removed to expose the DNA to RNA polymerase II and transcription factors. This is in contrast to PCR-generated DNA templates, which are free of nucleosomes, allowing the transcription factors and RNA polymerase II to easily access and bind to the DNA template for transcription initiation.