**4. Vitamin D receptor gene**

The human VDR (hVDR) gene is located at long arm of chromosome 12 bands 13-14 (12q13- 14) [101, 102]. The gene is 75 kb long and contains 11 exons [103]. This gene is divided into three regions: one coding region and two non-coding regions.

#### **4.1. Non‐coding regions**

The 5' promoter region of VDR lacks initiator (TATA and CAAT boxes) and is rich in GC content. It provides the putative site for binding of many transcription factors [103]. The promoter region is present at exon 1(1a, 1b, 1c, 1d, 1e, 1f). The promoter region facilitates the transcription activity of VDR target gene. The 3' UTR contains poly (A) repeats, which is reported to be associated with the mRNA stability.

#### **4.2. Coding region**

Coding region comprises of exon 2–9. Exon 2, which have translation start codons, contains DNA-binding site, whereas exon 7, 8 and 9 have ligand (vitamin D) binding site [104].
