Question 1

Why is competition for core enzyme so central here?

Accepted Answer

Because the sigma factors share one limited pool of core enzyme, so raising the level of any single sigma reduces the transcription driven by the others. A promoter whose output falls when a sigma is induced may simply have lost access to core, not lost its own regulator.

Question 2

What evidence assigns a promoter to a particular sigma?

Accepted Answer

Reconstituted transcription showing that defined holoenzyme carrying that sigma initiates at the promoter, together with in vivo comparison between a disruption strain and its parent under matched growth. Either line alone leaves room for indirect effects; the two together make the assignment defensible in a thesis chapter.

Question 3

Why must the sigma to core ratio be reported?

Accepted Answer

Because saturating sigma abolishes the competition that shapes promoter selection in the cell, so an in vitro result obtained under excess sigma may not describe anything that happens in vivo. Running a ratio series, and reporting where the behaviour changes, keeps the result connected to physiology.

Question 4

How should a stress shift experiment be timed?

Accepted Answer

With samples across the first minutes as well as later points, because sigma levels, holoenzyme formation and transcript accumulation each proceed on their own timescale. A single endpoint can miss the reallocation entirely. Stating the exact intervals and the harvest method makes the series reproducible elsewhere.

Question 5

Does a promoter sequence match settle recognition?

Accepted Answer

No. Sequence similarity to a consensus generates candidates, not conclusions, because spacer length, flanking sequence and upstream elements all shift how well a holoenzyme initiates. Predicted promoters need testing before they enter a regulon, and the prediction method should be reported alongside the tested subset.

Question 6

How are anti sigma effects separated from sigma abundance?

Accepted Answer

By measuring free sigma rather than total, since a factor held in an inhibitory partnership contributes nothing to transcription while still appearing on a blot. Comparing total level, partner level and promoter output from the same cultures distinguishes a change in supply from a change in availability.

Microbiology

Microbiology

Research Frontiers in Bacterial Sigma Factor Regulation and Promoter Specificity