期刊
ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS
卷 478, 期 1, 页码 18-25出版社
ELSEVIER SCIENCE INC
DOI: 10.1016/j.abb.2008.07.003
关键词
lectins; carbohydrate-binding proteins; RNA processing; RNA splicing; general transcription factor
资金
- GM-38740 [National Institutes of Health]
- Michigan State University Intramural Research [06-IRGP-858]
- National Science Foundation [MCB-0092919]
Galectin-1 (Gall) and galectin-3 (Gal3) are two members of a family of carbohydrate-binding proteins that are found in the nucleus and that participate in pre-mRNA splicing assayed in a cell-free system. When nuclear extracts (NE) of HeLa cells were subjected to adsorption on a fusion protein containing glutathione S-transferase (GST) and Gal3, the general transcription factor II-I (TFII-I) was identified by mass spectrometry as one of the polypeptides specifically bound. Lactose and other saccharide ligands of the galectins inhibited GST-Gal3 pull-down of TFII-I while non-binding carbohydrates failed to yield the same effect. Similar results were also obtained using GST-Gall. Site-directed mutants of Gall, expressed and purified as GST fusion proteins, were compared with the wild-type (WT) in three assays: (a) binding to asialofetuin-Sepharose as a measure of the carbohydrate-binding activity: (b) pull-clown of TFII-I from NE; and (C) reconstitution of splicing in NE depleted of galectins as a test of the in vitro splicing activity. The binding of GST-Gal1 (N46D) to asialofetuin-Sepharose was less than 10% of that observed for GST-Gal1(WT), indicating that the mutant was deficient in carbohydrate-binding activity. In contrast, both GST-Gal1(WT) and GST-Gal1(N46D) were equally efficient in pull-down of TFII-I and in reconstitution of splicing activity in the galectin-depleted NE. Moreover, while the splicing activity of the wild-type protein can be inhibited by saccharide ligands, the carbohydrate-binding deficient mutant was insensitive to Such inhibition. Together, all of the results suggest that the carbohydrate-binding and the splicing activities of Gal I can be dissociated and therefore, saccharide-binding, per se, is not required for the splicing activity. (c) 2008 Elsevier Inc. All rights reserved.
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