Repressor proteins play a crucial role in gene regulation by binding to specific DNA sequences and preventing the transcription of target genes. These proteins are encoded by regulator genes, not promoter, structural, or operator genes.

**Regulator Genes:**
- Regulator genes are responsible for encoding proteins that control the expression of other genes.
- They typically contain DNA sequences that serve as binding sites for regulatory proteins, including repressor proteins.
- These genes are involved in the regulation of gene expression by binding to the operator region of the DNA and blocking the binding of RNA polymerase to the promoter region.
- The binding of repressor proteins to the operator region prevents the transcription of target genes, thereby regulating their expression.

**Promoter Genes:**
- Promoter genes are responsible for encoding DNA sequences that are recognized by RNA polymerase.
- They are located upstream of the coding region of a gene and provide a binding site for RNA polymerase.
- Promoter sequences facilitate the initiation of transcription and are essential for gene expression.
- While promoter regions play a crucial role in gene regulation, they do not directly code for repressor proteins.

**Structural Genes:**
- Structural genes are responsible for encoding proteins that perform specific functions in an organism.
- These genes contain the coding sequence for the protein of interest.
- While structural genes are crucial for the production of proteins involved in various cellular processes, they do not directly code for repressor proteins.

**Operator Genes:**
- Operator genes are DNA sequences located near the promoter region of an operon.
- They serve as binding sites for repressor proteins and are involved in the regulation of gene expression.
- When a repressor protein binds to the operator region, it prevents the transcription of the genes within the operon.
- However, operator genes do not directly code for repressor proteins; they are regions of DNA that interact with repressor proteins.

In summary, repressor proteins are coded for by regulator genes, which are responsible for controlling the expression of other genes. Regulator genes contain DNA sequences that serve as binding sites for repressor proteins, allowing them to regulate gene expression by binding to operator regions and preventing transcription.