The RPA4 gene, encoding the 30-kDa subunit of the replication protein A (RPA) complex, plays a crucial role in DNA metabolism, particularly in DNA repair and the response to DNA damage. The following is an expanded overview, addressing your requests:

### 1. Associated Genes:
- **RPA1**: Forms a part of the canonical RPA complex with RPA2 and RPA3.
- **RPA2**: Another core subunit of the canonical RPA complex, involved in DNA replication and repair.
- **RPA3**: Complements the RPA complex with RPA1 and RPA2.
- **RAD51**: Involved in homologous recombination repair; RPA4 can associate with RAD51 during DNA damage response.
- **PCNA (Proliferating Cell Nuclear Antigen)**: A key player in DNA replication, which may cooperate with RPA4 in specific repair mechanisms.
- **RFC (Replication Factor C)**: Works alongside RPA in processes like DNA synthesis and repair.

### 2. Aging and Age-related Diseases:
While specific studies directly linking RPA4 to aging are limited, mutations or dysregulation in DNA repair mechanisms (of which RPA4 is a critical component) can contribute to aging and age-related diseases. Impaired DNA repair mechanisms are a hallmark of aging, and conditions such as cancer and neurodegenerative diseases may be associated with the function of RPA4 and the RPA complex. Some research has indicated that altered expression of genes involved in DNA repair can impact cellular senescence and genomic stability, which are crucial factors in the aging process.

### 3. Drug Interactions:
Currently, specific drugs that directly target RPA4 are not well-documented. However, given the role of the RPA complex in DNA replication and repair, inhibitors of DNA polymerases and agents affecting the DNA damage response pathway (such as:
- **Nucleotide analogs** (like gemcitabine or cytarabine which target rapidly dividing cells).
- **Poly(ADP-ribose) polymerase (PARP) inhibitors** (used in cancer therapy to exploit DNA repair deficiencies).

These types of drugs could interact indirectly with the functions of RPA4 due to its involvement in DNA repair mechanisms.

### 4. Pathways and Biological Processes:
RPA4 is involved in several critical biological pathways, including:
- **DNA Damage Response**: Participates in the recognition and repair of DNA double-strand breaks and single-strand breaks.
- **Replication Stress Response**: RPA4 helps stabilize and protect single-stranded DNA during replication and repair.
- **Nucleotide Excision Repair (NER)**: Plays a role in the dual incision/excision reactions vital for repairing distorted DNA.
- **Homologous Recombination**: RPA4 is involved in RAD51-mediated strand exchange, essential for the repair of DNA during meiosis and mitosis.
- **Cell Cycle Checkpoint Activation**: RPA4 helps facilitate various checkpoint controls during the cell cycle in response to DNA damage.

Overall, RPA4 is essential for maintaining genomic stability, making it a significant gene in cellular processes related to DNA repair and maintenance. Its functions are crucial for organismal health, particularly in contexts involving aging and DNA damage response.