The adenovirus E4-ORF4 splicing enhancer protein interacts with a subset of phosphorylated SR proteins.
SR proteins purified from uninfected HeLa cells inhibit adenovirus IIIa pre-mRNA splicing by binding to the intronic IIIa repressor element (3RE). In contrast, SR proteins purified from late adenovirus-infected cells are functionally inactivated as splicing repressor proteins by a virus-induced dephosphorylation. We have shown that the adenovirus E4-ORF4 protein, which binds the cellular protein phos phatase 2A (PP2A) and activates IIIa splicing in vitro and in vivo, induces SR protein dephosphorylation. Here we show that E4-ORF4 interacts with only a subset of SR proteins present in HeLa cells. Thus, E4-ORF4 interacts efficiently with SF2/ASF and SRp30c, but not with other SR proteins. Interestingly, E4-ORF4 interacts with SF2/ASF through the latter's RNA recognition motifs. Furthermore, E4-ORF4 interacts preferentially with the hyperphosphorylated form of SR proteins found in uninfected HeLa cells. E4-ORF4 mutant proteins that fail to bind strongly to PP2A or SF2/ASF do not relieve the repressive effect of HeLa SR proteins on IIIa pre-mRNA splicing in transient transfection experiments, suggesting that an interaction between all three proteins is required for E4-ORF4-induced SR protein dephosphorylation.
Estmer Nilsson
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C
Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, 751 23 Uppsala, Sweden.
Petersen-Mahrt
S
S
Durot
C
C
Shtrichman
R
R
Krainer
A R
AR
Kleinberger
T
T
Akusjärvi
G
G
D017504:Adenovirus E4 Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism*; D016366:Open Reading Frames; D010766:Phosphorylation; D011485:Protein Binding; D012326:RNA Splicing
D017504:Adenovirus E4 Proteins; D009363:Neoplasm Proteins