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E. coli DNA Polymerase I is a DNA-dependent DNA polymerase having 3′– 5' and 5′– 3′ exonuclease activity.

1-Nick DNA translation

2-Synthesis of the second strand of cDNA

Alternative (d) The transcription is given specificity by the Sigma unit ( $\mathrm{σ}$unit). Because it may attach and detach from the core enzyme, the RNA polymerase enzyme is a holoenzyme. The enzyme is directed to a specific binding or interaction site on DNA by this$\mathrm{σ}$ unit. It identifies promoter consensus sequences to assist RNA polymerase in binding to DNA. This subunit starts the transcription process and then separates from the enzyme after it's started.

$\mathrm{Î\pm }$Alpha unit (option a). RNA polymerase in prokaryotes is a holoenzyme. There are two units in this enzyme that are responsible for binding to promoter DNA and other transcription machinery factors.

$\mathrm{β}$-Beta unit (option b). RNA polymerase in prokaryotes is a holoenzyme. The B unit of RNA polymerase is the second biggest subunit, and it is responsible for RNA production by binding to ribonucleoside triphosphate.

$\mathrm{β}\text{'}$- Beta-dash unit (option c). The $\mathrm{β}\text{'}$unit is the biggest subunit of RNA polymerase, and it is responsible for attaching to the DNA template strand and actively synthesising RNA.