Alternate Translation Initiation Codons Can Create Functional Forms of Cystic Fibrosis Transmembrane Conductance Regulator (*)
- Tiziana Piazza Carroll,
- Marcelo M. Morales,
- Stephanie B. Fulmer,
- Sandra S. Allen,
- Terence R. Flotte,
- Garry R. Cutting and
- William B. Guggino(§)
- From the (1) Department of Physiology and Pediatrics and the Center for Medical Genetics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
- §To whom correspondence should be addressed: Dept. of Physiology and Pediatrics, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205. Tel.: 410-955-7166 or 410-955-4816; Fax: 410-955-0461; E-mail: wguggin{at}wpo.bs.jhu.edu.
Abstract
To evaluate the function of transmembrane domain 1 (TMD1) of the cystic fibrosis transmembrane conductance regulator (CFTR)
and the methionines that function in translation initiation, a series of progressive 5′ truncations in TMD1 were created to
coincide with residues that might serve as translation initiation codons. Expression of the mutants in Xenopus oocytes demonstrated that internal sites in TMD1 can function as initiation codons. In addition, all of the mutants that
progressively removed the first four transmembrane segments (M1-M4) of TMD1 expressed functional cAMP-regulated Cl
channels with ion selectivity identical to wild-type CFTR but with reduced open probability and single channel conductance.
Further removal of transmembrane segments did not produce functional Cl
channels. These data suggest that segments M1-M4 are not essential components of the conduction pore or the selectivity filter
of CFTR.
Footnotes
-
↵* This work was supported in part by National Institutes of Health Grants HL47122, HL51811, DK48977, and DK44003 and by the Cystic Fibrosis Foundation Research Development Program. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- CFTR
-
cystic fibrosis transmembrane conductance regulator
- TMD
-
transmembrane domain
- NBD
-
nucleotide binding domain
- IBMX
-
isobutylmethylxanthine
- DIDS
-
4,4′-diisothiocyanostilbene-2,2′-disulfonic acid
- WT
-
wild type.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
