The strain BX265 expresses the translational fusion waEx18(acs-4p::ACS-4::GFP). The strain was constructed using PCR to amplify the acs-4 genomic and promoter region (approximately 3 kb upstream of the ATG start site) and cloned into the pPD95.79 vector in frame to create a C terminal GFP fusion protein. The plasmid construct was microinjected into N2 worms and GFP positive worms were selected each generation to maintain the extrachromosomal array. Worms were viewed by confocal microscopy as described in Section 2.6.