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Mol Cell Biol, August 1998, p. 4863-4871, Vol. 18, No. 8
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Structure-Function Analysis of Qk1: a Lethal Point Mutation in Mouse quaking Prevents Homodimerization

Taiping Chen and Stéphane Richard*

Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, and Departments of Oncology, Medicine, and Microbiology and Immunology, McGill University, Montréal, Québec H3T 1E2, Canada

Received 17 February 1998/Returned for modification 24 March 1998/Accepted 18 May 1998

Qk1 is a member of the KH domain family of proteins that includes Sam68, GRP33, GLD-1, SF1, and Who/How. These family members are RNA binding proteins that contain an extended KH domain embedded in a larger domain called the GSG (for GRP33-Sam68-GLD-1) domain. An ethylnitrosourea-induced point mutation in the Qk1 GSG domain alters glutamic acid 48 to a glycine and is known to be embryonically lethal in mice. The function of Qk1 and the GSG domain as well as the reason for the lethality are unknown. Here we demonstrate that the Qk1 GSG domain mediates RNA binding and Qk1 self-association. By using in situ chemical cross-linking studies, we showed that the Qk1 proteins exist as homodimers in vivo. The Qk1 self-association region was mapped to amino acids 18 to 57, a region predicted to form coiled coils. Alteration of glutamic acid 48 to glycine (E&cjs3613;G) in the Qk1 GSG domain (producing protein Qk1:E&cjs3613;G) abolishes self-association but has no effect on the RNA binding activity. The expression of Qk1 or Qk1:E&cjs3613;G in NIH 3T3 cells induces cell death by apoptosis. Approximately 90% of the remaining transfected cells are apoptotic 48 h after transfection. Qk1:E&cjs3613;G was consistently more potent at inducing apoptosis than was wild-type Qk1. These results suggest that the mouse quaking lethality (E&cjs3613;G) occurs due to the absence of Qk1 self-association mediated by the GSG domain.

* Corresponding author. Mailing address: Molecular Oncology Group, Lady Davis Institute, 3755 Côte Ste-Catherine Rd., Montréal, Québec H3T 1E2, Canada. Phone: (514) 340-8260. Fax: (514) 340-7576. E-mail: mcrd{at}musica.mcgill.ca.

Mol Cell Biol, August 1998, p. 4863-4871, Vol. 18, No. 8
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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