Which is the “Only enzyme” that has “Capability” to catalyse Initiation, Elongation and Termination in the process of transcription in prokaryotes ?

The correct option is DNA dependent RNA polymerase.

Let's understand the process of transcription in prokaryotes and why this enzyme is responsible for all three stages (initiation, elongation, and termination):

1. Understanding Transcription in Prokaryotes:
Transcription is the process by which genetic information stored in DNA is copied into a complementary RNA strand. In prokaryotic organisms (such as bacteria), this process is relatively simple compared to eukaryotes and is carried out by a single type of RNA polymerase enzyme.

2. The Role of DNA-dependent RNA Polymerase:
In prokaryotes, a single DNA-dependent RNA polymerase catalyses the transcription of all types of RNA (mRNA, tRNA, and rRNA). It has the capability to perform all three phases of transcription:
• Initiation: The RNA polymerase (specifically the holoenzyme) binds to a specific region on the DNA template strand called the promoter. The transient association with the initiation factor (sigma factor, $\sigma$) assists the RNA polymerase in specifically recognizing the promoter region and initiating transcription.
• Elongation: Once transcription starts, the sigma factor is released, and the core RNA polymerase enzyme moves along the template DNA strand, synthesizing the RNA chain in the 5' to 3' direction using ribonucleoside triphosphates (NTPs) as substrates.
• Termination: When the enzyme reaches the terminator sequence on the DNA template, the synthesized RNA molecule and the RNA polymerase separate from the DNA. This termination is often assisted by the transient binding of a termination factor (rho factor, $\rho$).

3. Why other options are incorrect:
• DNA dependent DNA polymerase: This enzyme is primarily involved in DNA replication, where it synthesizes a complementary DNA strand from a DNA template, not transcription.
• DNA Ligase: This enzyme joins DNA fragments together by catalyzing the formation of phosphodiester bonds (e.g., joining Okazaki fragments during DNA replication or in DNA repair).
• DNase: This is a nucleolytic enzyme (deoxyribonuclease) that degrades DNA by hydrolyzing phosphodiester bonds; it is not involved in transcription synthesis.