THE USE OF DEFICIENCIES TO DETERMINE ESSENTIAL GENE CONTENT IN THE LET-56-UNC-22 REGION OF CAENORHABDITIS-ELEGANS

We have investigated the possibility of using the polymerase chain rea ction to detect deletions of coding elements in the unc-22-let-56 inte rval on chromosome IV in the nematode Caenorhabditis elegans. Our anal ysis of approximately 13 kb of genomic sequence immediately to the lef t of the unc-22 gene resulted in the identification of four possible g enes. Partial cDNAs have been identified for three of them. To determi ne whether any of these coding elements are essential for development, we required a method for the induction and selection of mutations in these elements. Our approach was to identify a set of formaldehyde and gamma radiation induced unc-22 mutations that mapped to the unc-22-le t-56 region, and then employ polymerase chain reaction methodology to identify deficiencies that affected one or more of the four identified coding elements. Two small deficiencies were identified in this manne r. Characterization of these deficiencies shows that there are no codi ng elements between unc-22 and let-56 (the nearest mutationally identi fied gene to the left of unc-22), which are required in development un der laboratory conditions. We conclude that the polymerase chain react ion is a practical tool for the detection of deletions of coding eleme nts identified in this region, and that characterization of such defic iencies provides a method for assessing whether or not these elements are required for development.