Which one of the following is not the part of transcription unit in DNA?

Initiation factor

The correct answer is Option (3) → Initiation factor   

The process of copying genetic information from one strand of the DNA into RNA is termed as transcription.However, unlike in the process of replication, which once set in, the total DNA of an organism gets duplicated, in transcription only a segment of DNA and only one of the strands is copied into RNA.

A transcription unit in DNA is defined primarily by the three regions in the DNA :
(i) A Promoter
(ii) The Structural gene
(iii) A Terminator

A) Promoter - This region signals the starting point of transcription and provides a binding site for RNA polymerase.

(C) Terminator - This region signals the end of transcription.

(D) The structural gene - This region contains the sequence that will be transcribed into RNA.

                                                          Schematic structure of a transcription unit