sup-10 is a member of a group of interacting genes that includes
unc-93 ,sup-g,
sup-10 ,sup-ll and
sup-18 (Greenwald and Horvitz, 1980, 1982, 1986). Rare altered function alleles of
unc-93 ,
sup-9 ,and
sup-10 confer a distinctive, muscle defective phenotype. When touched on the head, a mutant worm quickly contracts and then relaxes without moving backward as would a wild-type worm. This has been termed a "rubber band" phenotype. The regulation or coordination of muscle contraction appears to be defective in these animals. Null mutations in
unc-93 ,
sup-9 ,
sup-10 and
sup-18 are wild-type in phenotype on their own and act as recessive suppressors of the rubber band mutations (Greenwald and Horvitz, 1980, 1982, 1986). The
unc-93 gene encodes a putative transmembrane protein (Levin and Horvitz, 1992, J. Cell Biol. 117:143). Levin and Horvitz speculate that the
unc-93 protein might be a component of an ion transport system involved in excitation-contraction coupling in muscle or might be involved in the coordination of muscle contraction, perhaps by affecting the functioning of gap junctions. We have previously reported that
sup-10 and the regulatory myosin light chain (MLC) genes,
mlc-1 and
mlc-2 ,are linked on the X chromosome. In collaboration with Donna Albertson and Joshua Levin, we mapped
mlc-1 ,2to the right end of the X chromosome and demonstrated that a
mlc-1 ,2hybridization probe detected alterations in 6 of 40
sup-10 mutant strains originally tested. Initially, we predicted that
sup-10 was located within a short distance of the MLC genes. Localization of the
sup-10 gene by transformation rescue indicates that, in fact,
sup-10 is approximately 60kb rightward of the MLC genes. (The left-to-right gene order is
mlc-2 -
mlc-1 -
sup-10 ,defined with respect to the physical map.) We analyzed a number of
sup-10 mutant DNAs on Southern blots looking for clues as to the precise position of the
sup-10 gene. We detected blot phenotypes for 18
sup-10 mutants. Fifteen contain large homozygous viable deletions. For example,
sup-10 (
n184)removes most of
mlc-1 and extends rightward an estimated minimal distance of 180 kb. The remaining three
sup-10 mutants for which we have detected blot phenotypes were isolated in a
mut-2 background and contain Tc1 element insertions at three distinct positions within a region of approximately 350 bp. No other alterations have been observed for these 3 alleles. The leftward endpoint of the most distal of the deletions that confer a
sup-10 phenotype is located a short distance to the right of these insertions. It is likely that the Tc1 insertions and this deletion endpoint are located within the
sup-10 gene. We have achieved transformation rescue of
sup-10 in two ways. In both cases, we injected a cosmid, F57C11 , that flanks the sites of Tc1 insertion and the deletion endpoint to the right of the insertions. First, we rescued the suppression phenotype of
sup-10 .We coinjected F57C11 cosmid DNA with the
rol-6 dominant plasmid into an
unc-93 (
e1500);
sup-10 (
n184)strain. This strain has a wild-type phenotype.
e1500 is a rubber band allele of
unc-93 .
n184 completely deletes the
sup-10 gene. We reasoned that since suppression of
e1500 by
n184 is recessive, expression of a wild-type
sup-10 gene in a transformed animal should result in a rubber band phenotype. We have obtained a heritably transformed line of rubber band rollers that are Unc and completely egg-laying defective as are
e1500 animals. Loss of the array results in the segregation of wild-type non-roller animals. Second, we rescued the recessive rubber band phenotype of
sup-10 (
n983).We coinjected F57C11 cosmid DNA with the
rol-6 dominant plasmid into a
sup-10 (
n983)strain. We have obtained a heritable line of non-rubber band rollers indicating rescue of
n983 .These transformants segregate non-roller rubber band animals when the array is lost.