HUMAN RIBOSOMAL-PROTEIN L7 BINDS RNA WITH AN ALPHA-HELICAL ARGININE-RICH AND LYSINE-RICH DOMAIN

In this study we mapped the RNA-binding domain of human ribosomal prot ein L7 and characterized its conformation-dependent RNA-binding specif icity. Binding competition assays demonstrated preferential binding of L7 to mRNAs and rRNA, but not to tRNA. The ribohomopolymer poly(G) is bound with high affinity whereas poly(U), poly(C), or poly(A) show lo w affinity to L7. Furthermore, L7 binds to double-stranded but not to single stranded DNA. Deletion mapping showed that the RNA-binding doma in of L7 is represented by an arginine-rich and lysine-rich oligopepti de (ELKIKRLRKKFAQKMLRK-ARRK), which is reminiscent of the arginine-ric h motif (ARM) found in one family of RNA-binding proteins. The isolate d RNA-binding domain is capable of high affinity binding to the Rev-re sponsive element (RRE) of human immunodeficiency virus type 1 in vitro . Circular dichroic studies demonstrated a concentration-dependent and ligand-induced alpha-helical transition of a synthetic peptide carryi ng the arginine-lysine-rich RNA-binding domain of protein L7. Peptides carrying a mutation that destroys the alpha-helical conformation do n ot bind RNA.