Molecular Biology Answers

Is sigma factor a transcription factor?
After I googled 'sigma TF' I stumbled upon two papers(only).
From a paper:
Sigma factors (sigmas) are bacterial transcription factors that bind core RNA polymerase (RNAP) and direct transcription initiation at cognate promoter sites.
and another paper had the title -
Specific binding of the transcription factor sigma-54 to promoter DNA.
However this contradicts with my book- Principle of Genetics Snustard and Simmons:
'Unlike their prokaryotic counterparts, eukaryotic RNAPs cannot initiate transcription by themselves ....require the assistance of protein transcription factors to start synthesis.'
What's your opinion?

What does 'N utilisation' in NusA (N utilisation substance protein A) protein mean?

Does positive supercoiling promote negative supercoiling in uncoiledDNA?
I was reading a paper(for fig): https://www.researchgate.net/publication/6955430_Structural_basis_for_ATP-dependent_DnaA_assembly_and_replication-origin_remodeling
Stumbled upon this: As a right-handed ATP-DnaA spiral would be expected to wrap DNA into a positive supercoil, adjacent DNA regions would be subjected to compensatory negative writhe (Fig. 6d, left). Although any superhelical strain generated by DnaA-mediated wrapping would be expected to spread throughout the topological domain that contains the origin, it may preferentially affect the nearby DUE, which is unstable and prone to spontaneous unwinding.

I was reading Lehninger and stumbled upon the following:
By convention, if the links between two DNA strands are arranged so that the strands are interwound in a right-handed helix, the linking number is defined as positive (+); for strands interwound in a left-handed helix, the linking number is negative (-). Negative linking numbers are, for all practical purposes, not encountered in DNA.
By linking number they must be talking about twists. My question is since we have Z-DNA whose strands are in left-handed helix can't its Twist be negative?