Mutations in the
unc-23 gene cause a bent head phenotype, which is the result of dystrophy and detachment of the anterior body wall musculature (Waterston et al., Dev. Biol. 77:271 1980). Suppression of this phenotype is observed when
unc-23 animals are grown in liquid culture (A. Bullerjahn and D. Riddle, pers. comm.). Attachment of muscle to the underlying hypodermis is still fragile however, as a small amount of pressure applied to the animal results in detachment of the muscle cells from the underlying hypodermis. We have recently cloned
unc-23 and found that it encodes a domain similar to the molecular chaperone regulator BAG-2 (BCL2-associated athanogene 2). In mammals, the BAG family of molecular chaperone regulators, contain a conserved 45 amino acid region near their C termini (the BAG domain). Human BAG-2 and C. elegans UNC-23 share 40% amino acid identity and 62% similarity over the BAG domain and its upstream region. We have characterized the temporal and spatial expression pattern of UNC-23, using a full-length
unc-23::GFP construct that is capable of rescuing the
unc-23 phenotype. UNC-23 is expressed in a wide variety of tissues such as the body wall muscle cells, hypodermis, and pharynx. In mammals, BAG-2 binds the ATPase domain of Hsp70/Hsc70 and regulates the Hsp70 chaperone activity (Takayama et al., The Journal of Biological chemistry 274: 781,1999). Using a yeast two hybrid screen, we have identified the ATPase domain of HSP-1 as an interacting partner with the COOH terminus of UNC-23. We previously had identified two dominant suppressors of
unc-23(
e25) and here demonstrate that they are alleles of
hsp-1 . The molecular lesions that result in HSP-1 suppressor activity are missense mutations located within the ATPase domain of the molecule. These studies demonstrate an interaction between UNC-23 and HSP-1in C. elegans .