Identification of an erythroid-enriched endoribonuclease activity involved in specific mRNA cleavage

Stability of the human α–globin mRNA is conferred by a ribonucleoprotein complex termed the α–complex, which acts by impeding deadenylation. Using our recently devised in vitro decay assay, we demonstrate that the α–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 α–complex and is regulated by the presence of the α–complex. Similar endoribonuclease cleavage products were also detected in erythroid cells expressing an exogenous α–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 α–complex stabilizes the α–globin mRNA in erythroid cells by a multifaceted approach, one aspect of which is to protect the 3′–UTR from specific endoribonuclease cleavage