This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basics of DNA, Subject name: Biochemistry
Histone proteins are rich in which of the following amino acids? 
Select and explain. 
A. Histidine and lysine, B. Lysine and Arginine, C. Arginine and Histidine, D. Histidine and Valine
B: Lysine and Arginine
Answer: B: Lysine and Arginine 
Explanation: Histone proteins: Rich in positively charged amino acids, lysine and arginine. Carboxyl terminal 2/3rd of histone molecules are hydrophobic, Amino terminal 1/3rd are paicularly rich in basic amino acids. These amino terminal end protrude out of the octamer and is known as histone tail. Amino acids of histone tail undergo post-translational modifications.