This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
Transport across nucleus is by all except? 
Select and explain. 
A. Caveolins, B. Local signals, C. Importins, D. Rat proteins
D: Rat proteins
Answer: D: Rat proteins 
Explanation: Ans. d. Rat proteinsSource: InternetImportin - Type of karyopherinTransporting protein molecules into nucleus by binding to specific recognition sequences, called nuclear localization sequences (NLS).2 subunits, importin a and importin bCaveolinsFamily of integral membrane proteins that are principal components of caveolae membranes.Involved in receptor-independent endocytosis.Acts as scaffolding proteins within caveolar membranes by compart-mentalizing and concentrating signaling molecules.Rat proteins:Recombinant rat IFN--is a bioactive protein intended for use in cell culture applications.