Final answer:
The two types of effectors that can bind to repressor proteins are co-repressors and inducers; co-repressors enhance the repressor's ability to inhibit transcription, while inducers prevent the repressor from binding to the operator, therefore promoting transcription. Option d is correct.
Step-by-step explanation:
In the context of prokaryotic gene regulation, the question asks what two different types of effectors can bind to repressor proteins. The correct answer is d) Co-repressors and inducers. A co-repressor is a substance that can bind to a repressor protein, causing the repressor to bind more tightly to the operator, blocking transcription.
On the other hand, an inducer binds to a repressor and prevents it from binding to the operator, thus allowing gene transcription to take place. Both of these effectors play a crucial role in the regulation of gene expression in an operon.