This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Steriod recetor regulatory protein is: (PGI Dec 2006) 
Select and explain. 
A. Zinc finger, B. Helix-tum-helix, C. Leucine zipper, D. RNA
A: Zinc finger
Answer: A: Zinc finger 
Explanation: Ans: A (Zinc finger ) Three motifs mediate the binding of regulatory proteins to DNA. These are : helix- turn-helix, zinc finger & leucine zipper.Examples of transcription regulatory proteins that contain these motifsBinding MotifOrganismRegulatory ProteinHelix-turn-hetixE colilap repressor CAP Phagel cl, cno, and tryptophan and 434 repressors Mammalshomeo box proteins Pit-1, Oct l, Oct2Zinc fingerE coliGene 32 protein YeastGal4 DrosophillaSerendipity, Hunchback XenopusTFIIIA MammaisSteroid receptorQ family, Sn1Leucine zipperYeastGCN4 MammalsC/EBP, fos, jun, Fca-1, CRE binding protein, c-myc, n-myc, l-myc