What effect does the lambda repressor protein have in the prophage state?

The lambda repressor protein plays a crucial role in maintaining the lysogenic cycle of bacteriophage lambda by inhibiting the expression of certain genes that would lead to the lytic cycle. In the prophage state, the lambda repressor binds to specific operator sites in the viral DNA, thereby blocking the transcription of immediate early genes like Cro.

This repression of Cro synthesis is key because Cro protein is involved in promoting the lytic cycle, where the virus replicates and ultimately leads to cell lysis. By preventing the synthesis of Cro, the lambda repressor ensures that the viral genome remains integrated into the bacterial host's chromosome and that the prophage state is maintained. This mechanism allows the phage to reside dormant within the bacterial cell, replicating passively during bacterial cell division until it is triggered to enter the lytic cycle under certain environmental conditions.