Scientists Discover How Brain Encodes Memories

The production of new proteins can only occur when the RNA that will make the required proteins is turned on. Until then, the RNA is "locked up" by a silencing molecule, which is a micro RNA. The RNA and micro RNA are part of a package that includes several other proteins.

http://www.sciencecodex.com/ucsb_scientists_discover_how_the_brain_encodes_memories_at_a_cellular_level