I've come across two different definitions of negative and positive control of gene, and I'm not sure which one is the right one. The first one says:
"Positive control is accomplished by inducible systems, in which a repressor is removed from the operon by the inducer to promote transcription of a gene. Negative control is accomplished by repressible systems, in which a repressor–corepressor complex binds to the operon to prevent transcription. "
and another one says:
"Negative control is when gene is regulated by absence/presence of repressor, while a positive control is when a gene is regulated by absence/presence of an activator."
Which definition is right? and is lac operon an example of negative or positive control? Please help, I've looked all through online and MCAT study materials but they don't seem to agree at all and I'm confused.
"Positive control is accomplished by inducible systems, in which a repressor is removed from the operon by the inducer to promote transcription of a gene. Negative control is accomplished by repressible systems, in which a repressor–corepressor complex binds to the operon to prevent transcription. "
and another one says:
"Negative control is when gene is regulated by absence/presence of repressor, while a positive control is when a gene is regulated by absence/presence of an activator."
Which definition is right? and is lac operon an example of negative or positive control? Please help, I've looked all through online and MCAT study materials but they don't seem to agree at all and I'm confused.