what is the purpose of a negative transcription factor

Question

transcription factors work alone or with 

Answer 1

Noel has nicely explained the molecular mechanism of repressor,  an inhibitory transcription factor or a negative regulator of transcription.

 

In simplistic terms, they are like light switches that are turned off unless one needs light.Cells turn off certain genes unless they need it. That's how negative transcription factors work in plant and animal cells.

 

Hope this helps as well.

Answer 2

Negative transcription factors (repressors) prevent transcription of certain pieces of DNA. One example, is the suppression of the lac operon. In this case, the repressor is bound in the absence of lactose, but undergoes a conformational change when bound to lactose, and it "falls off" which allows transcription (and in turn, metabolism) to take place. In this specific case, the purpose of the negative transcription factor is to control metabolism of lactose.