For some time it was not clear whether lac repressor inhibits lac operon transcription by inhibiting the binding of RNA polymerase to its promoter or by allowing transcription initiation but blocking elongation past the site of bound repressor.

True.

Explanation:

The lac repressor is a molecule that is part of the regulation of genes to metabolize lactose to some bacteria, including Escherichia coli. Bacteria need to metabolize lactose to provide energy to your body, in which case the lac repressor acts as a lactose detector, preventing the genes responsible for lactose metabolism proteins from being activated unnecessarily, thereby preventing lactose digestion. The lac repressor has the opposite function to the lac operon, which stimulates lactose digestion.

However, for some time, it was unclear whether lac repressor inhibits lac operon transcription by inhibiting RNA polymerase binding to its promoter or allowing transcription to begin, but blocking elongation after the bound repressor site.

It is now recognized that lac repressor paralyzes enzyme production in the absence of lactose, and catabolic activator protein (CAP), which aids in the production of glucose in the medium.