Lethal mutations defining 112 complementation groups in a 4.5 Mb sequencedregion of Caenorhabditis elegans chromosome III

The central gene cluster of chromosome III was one of the first regions to be sequenced by the Caenorhabditis elegans genome project. We have performe d an essential gene analysis on the left part of this cluster, in the regio n around dpy-17III balanced by the duplication sDp3. We isolated 151 essent ial gene mutations and characterized them with regard to their arrest stage s. To facilitate positioning of these mutations, we generated six new defic iencies that, together with preexisting chromosomal rearrangements, subdivi de the region into 14 zones. The 151 mutations were mapped into these zones . They define 112 genes, of which 110 were previously unidentified. Thirtee n of the zones have been anchored to the physical sequence by polymerase ch ain reaction deficiency mapping. Of the 112 essential genes mapped, 105 are within these 13 zones. They span 4.2 Mb of nucleotide sequence. From the n ucleotide sequence data, 920 genes are predicted. From a Poisson distributi on of our mutations, we predict that 234 of the genes will be essential gen es. Thus, the 105 genes constitute 45% of the estimated number of essential genes in the physically defined zones and between 2 and 5% of all essentia l genes in C. elegans.