IDENTIFICATION OF AUF1 (HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN-D) ASA COMPONENT OF THE ALPHA-GLOBIN MESSENGER-RNA STABILITY COMPLEX

mRNA turnover is an important regulatory component of gene expression and is significantly influenced by ribonucleoprotein (RNP) complexes w hich form on the mRNA, Studies of human alpha-globin mRNA stability ha ve identified a specific RNP complex (alpha-complex) which forms on th e 3' untranslated region (3'UTR) of the mRNA and appears to regulate t he erythrocyte-specific accumulation of alpha-globin mRNA, One of the protein activities in this multiprotein complex is a poly(C)-binding a ctivity which consists of two proteins, (alpha CP1 and (alpha CP2. Nei ther of these proteins, individually or as a pair, can bind the alpha- globin 3'UTR unless they are complexed with the remaining non-poly(C) binding proteins of the alpha-complex, With the yeast two-hybrid scree n, a second alpha-complex protein was identified. This protein is a me mber of the previously identified A + U-rich (ARE) binding/degradation factor (AUF1) family of proteins, which are also known as the heterog eneous nuclear RNP (hnRNP) D proteins, We refer to these proteins as A UF1/hnRNP-D, Thus, a protein implicated in ARE-mediated mRNA decay is also an integral component of the mRNA stabilizing alpha-complex. The interaction of AUF1/hnRNP-D is more efficient with alpha CP1 relative to alpha CP2 both in vitro and in vivo, suggesting that the alpha-comp lex might be dynamic rather than a fixed complex, AUF1/hnRNP-D could, therefore, be a general mRNA turnover factor involved in both stabiliz ation and decay of mRNA.