Worm Breeder's Gazette 11(1): 41

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unc-4: 2 kb from ennui

David Miller, Medeva Ghee, Michelle Dubois, Thomas Burglin and Gary Ruvkun

Figure 1

unc-4 appears to define the wiring diagram for a specific portion of 
the ventral nerve cord.  In unc-4(e120), most VAn motor neurons assume 
a pattern of presynaptic connections normally reserved for the VBn 
motor neuron class; VAn's receive input from AVB and PVC interneurons 
as opposed to the normal sets of connections with AVA, AVD and AVE 
which are absent in e120 (White et al., WBG 9, p81, 1985).  We have 
now shown that unc-4 may correspond to yet another homeobox locus in C.
elegans.A spontaneous allele, unc-4(wd1), was isolated from the 
mutator strain TR679 in a general screen for movement-defective 
mutants.  Blots of recombinants with flanking markers rol-6 and bli-1 
identified two closely linked TC1-containing EcoRI fragments; wdP1 (2.
5 kb) is 0.12 m.u to the right and wdP3 (3.2 kb) is 0.1 m.u to the 
left.  A phage clone overlapping wdP1 was fingerprinted in Cambridge 
and maps to a large contig near unc-4 on chromosome II.  wdP3 includes 
repetitive DNA and a corresponding phage clone to mark the left side 
boundary is apparently not represented in our genomic library.
The identification of a homeobox sequence in the region, however, 
suggested a likely location for unc-4.  Cosmid C07E2 overlaps, ceh-4, 
one of 50 different homeobox loci that hybridize with a degenerate 
oligonuclcotidc probe (T.  Burglun and G.  Ruvkun, WBG 10, p35, 1988). 
We probed Southern blots of DNA isolated from 15 independent unc-4 
alleles with random primer labeled C07E2.  Alterations were detected 
in five of these alleles: e2314, e2320, e2308 (from M.  Shen), e887 
and wd-1.  All of these mutations affect a 1.8 kb EcoRI fragment (see 
below).  The e2320 mutation deletes 200 bp from the 1.8 kb fragment.  
In wd-1, the 1.8 kb as well as several other EcoRI fragments are 
absent suggesting a large deletion (~25kb).  The alterations observed 
in e2314, e2308, and e887 have not been reconstructed but all of these 
mutations delete the 1.8 kb EcoRI fragment.  A restriction map of the 
region indicates that a 1.05 kb EcoRI fragment containing the homeobox 
'third helix' consensus sequence (.WFQNRR.K.R) is adjacent to the 
region that is altered in unc-4 mutants.  We are now searching for a 
cDNA to determine if in fact the putative homeodomain corresponds to 
portion of the unc-4 coding sequence.
[See Figure 1]

Figure 1