Volume 18, no. 11, p. 6365-6373, 1998. Based on information kindly provided by Gerard Faye of the Institut Curie (Orsay, France), we have determined that the KIN28 gene used in two of our experiments (Fig. 3 and 6) contains two additional mutations that arose during PCR amplification of the sequence from a cDNA library. These mutations result in two amino acid changes in nonconserved regions of the Kin28 protein kinase sequence (N123D and M273T). Since this double mutant gene allows growth of kin28-3 cells and encodes a Kin28 protein with abundant kinase activity (Fig. 3 and 6), these two mutations do not abolish Kin28 function. However, the presence of these mutations does appear to have an impact on the requirement for T162 phosphorylation in Kin28 function. We showed in Fig. 3 that the T162A mutation blocks Kin28 function, suggesting that phosphorylation at this site might be required for full function. However, G. Faye (unpublished data) and M. Solomon's group (J. Kimmelman, P. Kaldis, C. J. Hengartner, G. M. Laff, S. S. Koh, R. A. Young, and M. J. Solomon, Mol. Cell. Biol. 19:4774-4787, 1999) have shown recently that the T162A mutation alone does not abolish Kin28 function. The explanation for this discrepancy appears to be that the two background mutations in our KIN28 gene have weakened the kinase to the extent that phosphorylation of T162 is now essential for function.

This error does not affect the major conclusions of the paper: Cak1 phosphorylates Kin28, and phosphorylation greatly enhances Kin28 activity in vivo and in vitro. We now believe, however, that the low basal activity of unphosphorylated Kin28 is sufficient for its essential function, although the absence of phosphorylation renders the kinase susceptible to other minor defects. We regret our error and apologize for any confusion it may have caused.