Abstract

Stability of the human -globin mRNA is conferred by a ribonucleoprotein complex termed the -complex, which acts by impeding deadenylation. Using our recently devised in vitro decay assay, we demonstrate that the -complex also functions by protecting the 3'-untranslated region (3'-UTR) from an erythroid-enriched, sequence-specific endoribonuclease activity. The cleavage site was mapped to a region protected by the -complex and is regulated by the presence of the -complex. Similar endoribonuclease cleavage products were also detected in erythroid cells expressing an exogenous -globin gene. Nucleotide substitution of the target sequence renders the RNA refractory to the endoribonuclease activity. Insertion of the target sequence onto a heterologous RNA confers sequence-specific cleavage on the chimeric RNA, demonstrating the sequence specificity of this activity. We conclude that the -complex stabilizes the -globin mRNA in erythroid cells by a multifaceted approach, one aspect of which is to protect the 3'-UTR from specific endoribonuclease cleavage.