Worm Breeder's Gazette 10(1): 38
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Two independent approaches to the study of muscle genes have converged to demonstrate that the sup-10 gene encodes a regulatory myosin light chain (MLC) protein. Sup-10, described by I. Greenwald and R. Horvitz (1986, Genetics 113: 63-72), is a member of a group of interacting genes involved in muscle structure and function. These genes include unc-93, sup-10, 500) and sup-10(n983) are rare alleles that confer a characteristic uncoordinated ('rubber band') muscle defective phenotype. Null alleles of unc-93, sup-10 and sup-18 are phenotypically wild-type and act as recessive suppressors of unc-93(e1500) and sup-10(n983). The wild-type null phenotype for four of the five genes and the patterns of cross-suppression suggest that these genes are members of a multi- gene family. We have been using transposon tagging to clone four of these genes. Alleles of sup-10, sup-9 and sup-18 were isolated from strains with unc-93(e1500) or sup-10(n983) in a mut-2(r459) background (see Levin and Horvitz, 1987 C. elegans meeting abstracts). We have identified 27 suppressor mutations: eight alleles of sup-9, 13 alleles of unc-93, one sup-18 allele and five alleles of sup-10. We have shown that one of the unc-93 alleles (e1500n1415) has a very closely linked Tc1 insertion. Of recombinants in the interval between daf-2 and dpy-17 (7mu), the extra Tc1 is present in all nine unc-93 (0) recombinants and absent in all 17 unc-93 (+) recombinants (p<0.7mu to the left and p<0.8mu to the right within 95% confidence limits; note that this gene is on an arm). We have cloned a 7 Kb EcoRI restriction fragment containing this Tc1 into a phage vector. We have examined one sup-9 allele and found no linked Tc1, Tc3 or Tc4. Other backcrossed sup-9 alleles are being examined. The C. elegans 'regulatory' MLC gene family consists of two gene copies mlc-1 and mlc-2, that are separated by 2.7 Kb. (see Cummins and Anderson, 1987 C. elegans meeting abstracts). Cosmid clones that cover mlc-1 and mlc-2 were identified by J. Sulston and A. Coulson. In situ hybridization of these clones to metaphase chromosomes indicated that these genes are located near the right end of the X chromosome. To define more precisely the position of the mlc-1 and mlc-2 genes, a mlc-1/mlc-2 plasmid clone was used to probe Southern blots of total genomic DNA from strains heterozygous for deficiencies in this region. Hybridizations were quantitated and the results indicated that mlc-1 and mlc-2 are located within the deletion interval defined by mnDf8 and mnDf42. sup-10 and nine other genes have been mapped within this interval. These results suggested the possibility that sup-20 encodes a myosin light chain protein. To test whether sup-10 encodes a myosin light chain protein, we have screened for MLC gene alterations in sup-10 mutants. A mlc-1/mlc-2 clone was used to probe Southern blots of total genomic DNA from 13 sup-10 alleles. Two of five sup-10 alleles isolated in a mut-2 background and three of eight gamma ray-induced alleles (seven isolated by I. Greenwald) exhibit altered Southern blot patterns (two insertions, one deletion, one apparent tandem duplication and one complex rearrangement). Each of the rearrangements affects the mlc-1 gene but not the mlc-2 gene. The C. elegans 'essential' MLC gene family consists of at least two members, only one of which has been cloned. The cloned gene, mlc-3, was mapped by in situ hybridization to linkage group III, 34-41% from one end. Both unc-93 and sup-18 are located in this region. We have examined 11 unc-93 alleles (nine isolated in a mut-2 background, including unc-93(e1500n1415) and two gamma ray-induced alleles). All of these have a wild-type hybridization pattern when probed with a cosmid that includes the mlc-3 gene. Thus, we think it unlikely that unc-93 encodes the mlc-3 gene product, but we will examine additional unc-93 alleles. We are currently investigating whether sup-18 is mlc- 3 and whether unc-93, nd to other members of the C. elegans 'essential' MLC gene family.