We have been working towards correlation of the genetic and physical maps within a small portion of LG III. Specifically, we have focused on a subregion of the central cluster of LG III bound by the markers
dpy-17 and
dpy-19, constituting approximately two m.u. and an estimated 760 genes. This interval is represented molecularly by a set of nearly 170 minimally overlapping cosmid clones. With respect to the
dpy-17 to
dpy-19 region, our laboratory has both generated a comprehensive set of deficiencies and mutationally identified over 60 essential genes (see abstract by H. Steward et al., this meeting). In an attempt to correlate the physical and genetic maps within the
dpy-17 to
dpy-19 interval, we have designed 30 PCR primer pairs from 30 cosmids occupying various positions along the minimally overlapping set of clones utilized by the C. elegans sequencing consortium. Using these primers, we are mapping the breakpoints of a small deficiency set within this defined region. This assay has resulted in the placement of several anchors along the physical and genetic maps within the
dpy-17 to
dpy-19 interval. These anchor points will prove invaluable in furthering our attempts in using germline transformation techniques to rescue essential mutations within this region, and ultimately assign each of our mutationally identified essential genes to sequence inferred coding elements. As an illustration of the resolving power of these anchors, we have utilized the genetic map of this region and the LG III cosmid transgenic library (see abstract by D. Janke et. al., this meeting) to place
srl-2 on the physical map. Mutations at the
srl-2 locus suppress lethality of some recessive alleles of
rol-3 (V). All known alleles of
srl-2 are recessive and have no obvious phenotype in the absence of a sensitive genetic background, with the exception of mild effects on male tail morphology. Three factor mapping of
srl-2 places it close, but to the right of
sma-3, covered by sDp8 and within the deficiencies sDf127 and sDf135. Our PCR mapping data suggested that
srl-2 was likely within the region spanned by the cosmids B0361 and T20B12. Using a small set of the cosmid transgenic library known to constitute a minimally overlapping span of contiguous cosmid clones, we were able to show that
srl-2 likely resides within the overlap region of the B0361 and F56C9 (see abstract by W. B. Barbazuk et al,this meeting). This work was supported by grants from NSERC to D.L. Baillie and CGAT to A.M. Rose and D.L. Baillie, and a Medical Council Research Studentship to W. Bradley Barbazuk.