The
unc-13 gene is located 0.025 mu to the right of
unc-15 on the centre of LG I. The mutants have a distinctive phenotype; paralysed, kinky and small, and show irregular pharyngeal pumping. More than 30 alleles, including 5 amber mutants, have been isolated and the genetic analysis has been well investigated. It is curious that
unc-13(
e309) allele is specifically suppressed by
sup-6 mutation which is located on LG II, and which does not suppress amber or ochre mutation. In the last gazette, we reported, based on an EM serial reconstruction of a part of ventral cord, that the largest pair of interneurons in the ventral cord of
unc-13(
e450), AVAL and AVAR, had wrong gap junctions to the excitatory motoneurons of the classes VB and DB, as a major lesion. Towards understanding a molecular mechanism to specify neural connectivity, we have cloned the
unc-13 gene as a first step. The strategies employed were as follows: 1) We identified the location of
unc-15 gene on 'the genome map' by walking one step both sides of Paramyosin DNA which was isolated by Hiroaki Kagawa. 2) Using Southern hybridization of a set of cosmid clones to a semi- balanced sDf6/unc-15
(e73) genomic DNA, the orientation of the contig on the genetic map was determined by locating the sDf6 deletion end point which is located in between
unc-15 and
unc-13 on the genetic map.