The TK1 gene, encoding thymidine kinase 1, plays a crucial role in nucleotide metabolism, particularly in the salvage pathway for dTTP synthesis necessary for DNA replication. Below are additional details based on your request:

### 1. Associated Genes
The TK1 gene may function in conjunction with several other genes involved in nucleotide metabolism and DNA synthesis, particularly those in the salvage pathways or the de novo synthesis pathways. Some of the genes that have been associated with TK1 include:
- **DHFR (Dihydrofolate Reductase)**: Involved in the supply of nucleotides through folate metabolism.
- **TK2 (Thymidine Kinase 2)**: Another member of the thymidine kinase family involved in mitochondrial nucleotide metabolism.
- **RRM1 (Ribonucleotide Reductase M1)**: Plays a role in the conversion of ribonucleotides to deoxyribonucleotides, thus it is closely related to processes that involve TK1.
- **UMP-CMP Kinase (UMP-CMPK)**: Involved in nucleotide synthesis pathways.
- **POLA1 (DNA Polymerase Alpha 1)**: Important for DNA replication, especially in conjunction with dTTP availability.

### 2. Aging and Age-Related Diseases
Several studies have indicated that TK1 levels are associated with cellular activity in relation to aging:
- **Cancer**: Elevated TK1 levels have been linked to a range of cancers. As cells age, their ability for DNA repair and replication might decline, leading to alterations in TK1 expression.
- **Age-Related Diseases**: The dysregulation of TK1 could potentially contribute to the development or progression of age-related diseases such as chronic inflammatory conditions and metabolic syndromes, although specific mechanisms are still under investigation.
- **Cell Cycle Regulation**: TK1's expression is tightly controlled during the cell cycle, particularly in the S phase. Disruptions in this regulation may lead to senescence or contribute to age-related cellular changes.

### 3. Drug Interactions
TK1 interacts with several drugs, particularly those used in cancer therapy and antiviral treatments:
- **Nucleoside Analogs**: Such as:
  - **1-β-D-Arabinofuranosylcytosine (AraC)**: A chemotherapy drug requiring TK1 for its activation.
  - **3-Azido-3-deoxythymidine (AZT)**: An antiretroviral medication that also needs activation by TK1 to exert effects against HIV.
- **General Antiviral Agents**: TK1 may also influence the efficacy of various antiviral nucleoside analogs due to its role in nucleotide metabolism.

### 4. Pathways and Biological Processes
TK1 is involved in various important biological processes and pathways:
- **Nucleotide Salvage Pathway**: Specifically in the conversion of thymidine to thymidine monophosphate (dTMP), which is crucial for dTTP synthesis.
- **DNA Replication**: Plays a vital role during the S phase of the cell cycle, where DNA synthesis occurs.
- **Cell Cycle Regulation**: TK1 expression is tightly regulated during the cell cycle and is often used as a marker for cellular proliferation status.
- **Response to DNA Damage**: Influences the ability of the cells to respond to and repair DNA damage due to its role in supplying nucleotides for DNA repair mechanisms.

In summary, TK1 is a pivotal gene in nucleotide metabolism, with its expression being closely tied to the cell cycle and implicated in both cancer biology and aging-related processes. Its association with various drugs further underscores its clinical relevance in both cancer and antiviral treatment strategies.