APH-1 is a core component of the <font face=symbol>g</font>-secretase complex that is responsible for the intramembranous cleavage of many substrates, including the Notch receptor. Mutations in
aph-1 cause Notch-like phenotypes throughout the development of C. elegans. The evolutionarily conserved APH-1 protein contains seven transmembrane domains; in C. elegans a non-conserved 30 a.a. C-terminal cytoplasmic tail exists. Truncation of this tail (through the nonsense mutation
zu147) drastically reduces, but does not completely eliminate,
aph-1 function in the early embryo. Our immunofluorescence analysis demonstrates that APH-1 protein levels are reduced in these embryos, but interestingly we find that the small amount of detectable protein is predominantly perinuclear rather than at the plasma membrane, where it is found in wild-type embryos. Several studies have led to the notion that movement of the <font face=symbol>g</font>-secretase components to the plasma membrane is dependent on proper complex assembly in the early secretory pathway. We consider the possibility that the truncated APH-1 may be inefficient at assembling with other <font face=symbol>g</font>-secretase components to form a mature complex, and we analyze whether this situation is ameliorated in two separate cases of extragenic suppression of the
aph-1(
zu147) mutant phenotype. Mutation of the nonsense-mediated decay system (smg genes) provides an effective way of suppressing the
aph-1(
zu147) mutation, presumably by stabilizing the
aph-1(
zu147) mRNA that contains a premature stop codon. Indeed, we find elevated levels of APH-1 protein in
smg-3 mutant embryos. However, although a small amount of protein is detected at the plasma membrane in
smg-3 embryos, the vast majority of APH-1zu147 remains perinuclear, consistent with the model that truncated APH-1 is inefficient at complex assembly. A second, and independent means of restoring Notch signaling to
aph-1(
zu147) mutant embryos is through mutation of a new gene,
sao-1. The predicted SAO-1 protein sequence does not reveal its molecular role, however we present evidence that SAO-1 interacts with the E3 ubiquitin ligase SEL-10, suggesting involvement in protein turnover or trafficking. We asked whether the
sao-1 mechanism of suppression affects the subcellular distribution of APH-1, and found that in
sao-1 mutant embryos APH-1zu147 was no longer predominantly perinuclear, suggesting an effect on the turnover or trafficking of APH-1zu147. We will compare and contrast the levels and behavior of the truncated APH-1 protein in these two independent mechanisms of suppression, and also extend our analysis to assess whether the subcellular distribution of another <font face=symbol>g</font>-secretase component, APH-2, is affected in these mutant embryos.