# DBT JRF 2022 — Question 129

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Protein Motifs - Leucine Zipper · Difficulty: Medium

## Question

Which family of proteins has the greatest likelihood of containing a Leucine-zipper motif?

## Options

- **A.** Serine proteases
- **B.** Map kinases
- **C.** Transcription factors
- **D.** Sugar binding proteins

## Answer

Option C

## Explanation

Leucine zipper motifs in transcription factors: Leucine zippers are dimerisation motifs in a class of transcription factors (bZIP family): Structure: • A stretch of ~4–5 LEUCINE residues spaced exactly 7 positions apart (every 2 turns of an $\alpha$ -helix, since helices have 3.5 residues/turn). • These Leu residues are on the SAME face of the helix, forming a hydrophobic stripe. • Two such helices from partner proteins can interdigitate their leucine side chains (like a zipper closing) → coiled-coil dimer formation. • Adjacent to the leucine zipper is a basic region that contacts DNA (bZIP = basic Leucine Zipper). Examples of bZIP transcription factors: • c-Fos/c-Jun (AP-1 complex): oncoproteins • CREB (cAMP Response Element-Binding protein) • GCN4 (yeast) — the prototypical leucine zipper TF Leucine zippers are NOT found in serine proteases, MAP kinases, or sugar-binding proteins. Answer: Leucine zipper motifs are dimerisation domains found predominantly in bZIP transcription factors.

Source: https://mypyqbuddy.com/questions/which-family-of-proteins-has-the-greatest-likelihood-6a104cd5920734408bc0c790