Essential multidomain scaffolding protein required for normal development (Probable). Recruits channels, receptors and signaling molecules to discrete plasma membrane domains in polarized cells (By similarity). Required for proper embryonic elongation. Acts upstream of ajm-1 and becomes localized to apical junctions independently of ajm-1. With let-413, cooperatively regulates ajm-1 localization to apical junctions (PubMed:11715019, PubMed:18411252). Homooligomerizes; requires L27 domain (PubMed:18411252). Interacts (via L27 domain) with ajm-1; the interaction regulates ajm-1 apical junction location (PubMed:11715019, PubMed:18411252). Localizes at the apical junctions (PubMed:11715019, PubMed:18411252). Localization at the adherens junctions requires PDZ domains, lateral distribution requires SH3 domain and is let-413 dependent (PubMed:18411252). Expressed in the apical junctions in the hypodermis. PDZ domains are required for localization at the adherens junctions. SH3 domain is necessary for let-413 dependent lateral distribution. L27 domain is responsible for homooligomerization and interaction with ajm-1. Mutant embryos have elongation arrested immediately before or at the 2-fold stage. They display a large vacuole in the posterior region. Belongs to the MAGUK family.