Identification of two KH domain proteins in the alpha-globin mRNP stability complex.
Accumulation of globin mRNAs during erythroid differentiation is dependent on their extraordinary stability. The longevity of human alpha-globin mRNA is associated with a ribonucleoprotein complex (alpha-complex) formed on the 3' untranslated region (3'UTR). One or more of the proteins within this alpha-complex contain strong polycytosine [poly(C)] binding (alpha PCB) activity. In the present report we purify alpha PCB activity from human erythroid K562 cells. Although not able to bind the alpha-globin 3'UTR directly, alpha PCB activity is sufficient to complement alpha-complex formation in a cytosolic extract depleted of poly(C) binding activity. Peptide microsequencing demonstrates that alpha PCB activity contains two structurally related poly(C) binding proteins. These two proteins, alpha-complex protein (alpha CP)-1 and -2, have an overall structural identity of 80% and contain three repeats of the K homology (KH) domain which is found in a subset of RNA binding proteins. Epitope-tagged recombinant alpha CP-1 and alpha CP-2 expressed in cells are each incorporated into the alpha-complex. We conclude that alpha CP-1 and alpha CP-2, members of the KH domain RNA binding protein family, are involved in formation of a sequence-specific alpha-globin mRNP complex associated with alpha-globin mRNA stability. As such this represents the first example of a specific function for this class of proteins and suggests potential roles for other members of this protein family.
Kiledjian
M
M
Howard Hughes Medical Institute, Department of Genetics, Philadelphia 19104-6145, USA.
Wang
X
X
Liebhaber
S A
SA
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D005914:Globins / Q000096:biosynthesis*; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011066:Poly C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014407:Tumor Cells, Cultured
D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D011066:Poly C; D005914:Globins