The murine IgM secretory poly(A) site contains dual upstream and downstream elements which affect polyadenylation.
Regulation of polyadenylation efficiency at the secretory poly(A) site plays an essential role in gene expression at the immunoglobulin (IgM) locus. At this poly(A) site the consensus AAUAAA hexanucleotide sequence is embedded in an extended AU-rich region and there are two downstream GU-rich regions which are suboptimally placed. As these sequences are involved in formation of the polyadenylation pre-initiation complex, we examined their function in vivo and in vitro . We show that the upstream AU-rich region can function in the absence of the consensus hexanucleotide sequence both in vivo and in vitro and that both GU-rich regions are necessary for full polyadenylation activity in vivo and for formation of polyadenylation-specific complexes in vitro . Sequence comparisons reveal that: (i) the dual structure is distinct for the IgM secretory poly(A) site compared with other immunoglobulin isotype secretory poly(A) sites; (ii) the presence of an AU-rich region close to the consensus hexanucleotide is evolutionarily conserved for IgM secretory poly(A) sites. We propose that the dual structure of the IgM secretory poly(A) site provides a flexibility to accommodate changes in polyadenylation complex components during regulation of polyadenylation efficiency.
Phillips
C
C
Department of Medical Genetics, Uppsala University, Biomedical Centre, Box 589, SE-751 23 Uppsala, Sweden.
Virtanen
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A
D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D007075:Immunoglobulin M / Q000096:biosynthesis* / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D011061:Poly A; D016133:Polymerase Chain Reaction; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000096:biosynthesis; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D012322:RNA Precursors; D012333:RNA, Messenger; C033027:secretory IgM; D011061:Poly A