Final answer:
The incorrect statement is that sigma factor is required for both eukaryotic and prokaryotic transcription. Sigma factors assist prokaryotic RNA polymerase in transcription initiation, whereas eukaryotes have different transcriptional mechanisms involving multiple transcription factors and enhancers.
Step-by-step explanation:
The statement that is not true is: "Sigma factor is required for both eukaryotic and prokaryotic transcription." Sigma factors are associated with prokaryotic transcription, not eukaryotic.
Sigma factors are essential proteins that aid RNA polymerase in initiating transcription in prokaryotes. They are part of the prokaryotic RNA polymerase holoenzyme that binds to specific promoter sequences, allowing the precise initiation of transcription. In contrast, eukaryotic transcription involves a range of transcription factors and a complex machinery, including enhancers, but not sigma factors, due to the different organization and compartmentalization of the eukaryotic cell. Eukaryotic transcription factors aid in the assembly of the initiation complex at promoters and can work with enhancers to regulate gene expression. For instance, eukaryotic transcription is also regulated by the packaging of DNA around histones, which affects the accessibility of the DNA to the transcription machinery.