Which is not a part of a transcription unit in DNA ?

Inducer

Among the options provided, "Inducer" is not a part of a transcription unit in DNA.

A transcription unit in DNA refers to the segment of DNA that is transcribed into RNA. It includes several components:

1. Promoter: A promoter is a DNA sequence located upstream of a gene that initiates the process of transcription by providing the binding site for RNA polymerase, which begins the synthesis of RNA from the DNA template.
2. Structural gene: The structural gene contains the DNA sequence that encodes the information to produce a functional RNA molecule such as messenger RNA - mRNA, ribosomal RNA - rRNA, or transfer RNA - tRNA) . It includes exons that code for the final RNA or protein product.
3. Terminator: The terminator is a DNA sequence that signals the end of transcription. It prompts the RNA polymerase to stop transcription and release the newly formed RNA molecule.

The term "Inducer" generally refers to a substance or molecule that induces or triggers the expression of certain genes. Inducers can activate gene expression by interacting with regulatory elements, but they themselves are not a part of the transcription unit in DNA. Instead, they regulate gene expression by influencing transcription factors or regulatory proteins that control the activation or repression of specific genes.

Therefore, among the components listed, "Inducer" is not a part of the transcription unit in DNA; rather, it functions as a regulator of gene expression.