Multiple features contribute to the use of the immunoglobulin M secretion-specific poly(A) signal but are not required for developmental regulation.
The secretory-specific poly(A) signal (mus) of the immunoglobulin mu gene plays a central role in regulating alternative RNA processing to produce RNAs that encode membrane-associated and secreted immunoglobulins. This poly(A) signal is in direct competition with a splice reaction, and regulation requires that these two reaction efficiencies be balanced. The mus poly(A) signal has several unique sequence features that may contribute to its strength and regulation. Site-directed mutations and small internal deletions made in the intact mu gene show that an extensive AU/A-rich sequence surrounding AAUAAA enhances signal use and that, of the two potential downstream GU-rich elements, both of which appear suboptimally located, only the proximal GU-rich sequence contributes substantially to use of this signal. A GU-rich sequence placed at a more standard location did not improve mus poly(A) signal use. All mu genes tested that contained modified mus poly(A) signals were developmentally regulated, indicating that the GU-rich sequences, the sequences between them previously identified as suboptimal U1A binding sites, and an upstream suboptimal U1A site do not contribute to mu mRNA processing regulation. Expression of wild-type and modified mu genes in HeLa cells overexpressing U1A also failed to demonstrate that U1A contributes to mus poly(A) signal regulation.
Peterson
Martha L
ML
Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky, 800 Rose St., 108A Combs Building, Lexington, KY 40536-0096, USA. mlpete01@uky.edu
Bingham
Gina L
GL
Cowan
Clarissa
C
D000818:Animals; D001483:Base Sequence; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006367:HeLa Cells; D006801:Humans; D007075:Immunoglobulin M / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D050810:Octamer Transcription Factors / Q000235:genetics; D010950:Plasma Cells / Q000378:metabolism; D011061:Poly A / Q000235:genetics / Q000378:metabolism*; D039104:RNA 3' Polyadenylation Signals / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics
D007075:Immunoglobulin M; D050810:Octamer Transcription Factors; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; C075339:U1A protein; D011061:Poly A; D012321:DNA-Directed RNA Polymerases