Molecules that affect Gene expression, by affecting DNA transcription

• Direct interaction
• ...

.........

• Repressor
• Activator
• Inducers: affect the binding affinity of other transcription factors.

https://en.wikipedia.org/wiki/Transcription_factor

Sigma factor

Sigma factor binds before RNA polymerase binds. Several kinds of sigma factors.

Many transcription factors affect the sigma factor binding site, affecting the probability of RNA polymerase binding.