Supplemental Results and Discussion Properties of Two lin-3 Alleles

Previous results indicated that two lin-3 partial lf alleles, e1417 and n378, could not suppress the Muv phenotype of several SynMuv strains (Ferguson et al., 1987; Lu and Horvitz, 1998). Our tests using the two alleles are consistent with the previous reports (Supplementary Table S2). This could be explained by that the mutant genes still provide significant level of the activity of LIN-3 protein, which is clearly indicated by the fact that these alleles, unlike the null alleles (Ferguson and Horvitz, 1985; Liu et al., 1999), are viable and fertile. Ferguson et al (1987) also observed that in a lin-3(n378)/lin-3(n1059, null); lin-15(n765) strain, the Muv phenotype of the lin-15 allele was lower than that in a gonad-ablated lin-15(n765). This result is consistent with that the SynMuv phenotype is sensitive to the level of lin-3 activity. The genetic properties of e1417 and n378 alleles are consistent with their molecular lesions. e1417 contains a G to A substitution in a region just 5 ’ to the second promoter and severely abolishes the expression of lin-3 in the anchor cell (Hwang and Sternberg, 2004). n378 has a missense mutation causing the substitution of Glu21 to Lys (Liu et al., 1999). Since Glu21 is the first amino acid after the signal sequence of the extracellular domain that is expected to be removed during the maturation of the protein, n378 was hypothesized to cause a significant reduction of the LIN-3 protein level on the cell surface (Liu et al., 1999)