Nature 404, 289–293 (2000).

In this Letter, we used strain MT2124, the standard let-60(n1046gf) strain maintained in the Caenorhabditis Genetics Center, for odour-chemotaxis assays. However, we have found that this strain carries a side mutation(s) that profoundly impairs chemotaxis to the odorant isoamyl alcohol, indicating that we need to re-evaluate our conclusion from the results shown in Fig. 1 that the let-60(n1046gf) mutant has a reduced efficiency of odorant chemotaxis. We outcrossed MT2124 to the wild-type N2 and obtained two let-60(n1046gf) strains, JN130 and JN131. We also outcrossed the MT4866 strain, the let-60(n2021lf) strain used in the study, and obtained the JN148 strain. All the outcrossed strains show reduced chemotaxis to the two odorants tested, isoamyl alcohol and diacetyl, at low odorant concentrations (T.H. and Y.I., unpublished results). The chemotaxis defects are comparable in extent to, or slightly weaker than, the original MT4866 let-60(n2021lf) strain. Our conclusion that both inactivation and hyperactivation of LET-60 Ras cause reduced chemotaxis therefore remains unchanged. However, the result shown in Fig. 1d, which suggested that ksr-1(lf), mek-2(lf) and mpk-1(lf) suppress let-60(n1046gf), is no longer valid because outcrossed let-60(n1046gf) strains do not show chemotaxis defects at the odorant concentration used in Fig. 1d (1 × 10-3 dilution of isoamyl alcohol).