Identification of an erythroid-enriched endoribonuclease activity involvedin specific mRNA cleavage

Stability of the human alpha-globin mRNA is conferred by a ribonucleoprotei n complex termed the alpha-complex, which acts by impeding deadenylation. U sing our recently devised lit vitro decay assay, we demonstrate that the al pha-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 alpha-complex and is regulated by the presence of the alpha-complex. Similar endoribonucleas e cleavage products were also detected in erythroid cells expressing an exo genous alpha-globin gene. Nucleotide substitution of the target sequence re nders 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 activi ty. We conclude that the alpha-complex stabilizes the alpha-globin mRNA in erythroid cells by a multifaceted approach, one aspect of which is to prote ct the 3'-UTR from specific endoribonuclease cleavage.