Worm Breeder's Gazette 10(3): 46

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

The deg-1 Gene May Encode a Membrane Protein

Eve Wolinsky and Marty Chalfie

The deg-1(u38) mutation results in swelling and degeneration of 
certain neurons (including the PVC cells, whose deaths impart a tail 
touch insensitive phenotype).  The swelling of the affected cells 
suggests some type of membrane defect which eventually allows water to 
enter the cell.  We have found that the deg-1 gene product may in fact 
be an integral membrane protein.  This conclusion is based on cDNA 
sequence analysis (described below).  Localization of the deg-1 gene 
product to the cell membrane is consistent with the idea that the deg-
1 induced degenerations result from a membrane defect.  We have been 
sequencing three cDNA's obtained from the Ahringer/Kimble 'L1' library.
All three hybridize to the same genomic fragment of the deg-1 gene 
under stringent conditions.  The three cDNA's appear to represent 
transcripts which have undergone different sets of splicing events.  
All.three contain long stretches of identical sequence, which supports 
the conclusion that they represent transcripts of the same gene, 
rather than transcripts of other members of a hypothesized deg-1 gene 
family (see our abstract in last WBG).  One of the cDNA's, described 
in June at the Boston meeting, contains a deduced open reading frame 
encoding at least 340 amino acids.  Hydrophobicity plots of the 
translated protein indicate two possible membrane spanning segments, 
located between residues 191 to 231 and residues 275 to 316.    Eleven 
of the fifteen cysteine residues present in the sequence are located 
in the first 191 residues, upstream of the first hydrophobic region.  
It is possible that the first 191 amino acids are part of an 
extracellular domain, since intracellular conditions do not favor 
cross-linking of cysteines.  This cDNA does not contain a poly A tail. 
The second cDNA may be the most likely to represent a mature 
transcript, since it contains a poly A region of about sixty bases 
following a poly A addition site.  This cDNA contains an open reading 
frame encoding 338 amino acids, which is nearly identical to that of 
the first cDNA, with two important exceptions.  The first difference 
is a 72 base insertion that would result in a novel 24 amino acid 
sequence following amino acid 176 of the protein encoded by the first 
cDNA.  Second, the termination codons and poly A tail of the second 
cDNA occur at the end of the second possible membrane spanning region 
encoded by the first cDNA.  This would result in a protein at least 
twenty five amino acids shorter than that encoded by the first cDNA.  
The two cDNA's are probably identical at their 5' ends.  However, it 
is possible that both are incomplete due to the usual imperfections of 
cDNA libraries.  The third cDNA appears to represent an incompletely 
spliced transcript.  It contains relatively short open reading frames (
some of which encode sequences found in the proteins translated from 
the first two cDNA's).  These are flanked by A/T rich intron-like 
regions.  Consensus splice sites can be found at several intron/exon 
junctions.  Comparison of the sequences of the three cDNA clones 
suggests that deg-1 transcripts may be processed to produce different 
splicing patterns.  In the case of the first two cDNA's, splicing 
differences would result in different exon usage and different protein 
products.  It is also possible that the differences between the cDNA's 
arose as artifacts of library construction or subsequent cloning 
events.  We plan to perform RNA protection experiments to see if 
multiple forms of deg-1 transcripts can in fact be isolated from wild 
type worms and from deg-1 mutants.  The putative deg-1 protein 
sequences do not show significant homology to proteins in the data 
bases screened so far.