A NOVEL GLUTAMINE-RNA INTERACTION IDENTIFIED BY SCREENING LIBRARIES IN MAMMALIAN-CELLS

The arginine-rich motif provides a versatile framework for RNA recogni tion in which few amino acids other than arginine are needed to mediat e specific binding. Using a mammalian screening system based on transc riptional activation by HIV Tat, we identified novel arginine-rich pep tides from combinatorial libraries that bind tightly to the Rev respon se element of HIV. Remarkably, a single glutamine, but not asparagine, within a stretch of polyarginine can mediate high-affinity binding. T hese results, together with the structure of a Rev peptide-Rev respons e element complex, suggest that the carboxamide groups of glutamine or asparagine are well-suited to hydrogen bond to G-A base pairs and beg in to establish an RNA recognition code for the arginine-rich motif. T he screening approach may provide a relatively general method for scre ening expression libraries in mammalian cells.