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Premature aging of yeast cells that lack protein N-myristoylation. Shown here is a multilabel immunofluorescence analysis of yeast cells with a temperature-sensitive NMT1 allele. Cells are stained with DAPI to visualize nuclear DNA (purple); nucleoli are visualized as red (right), and Sir3p is visualized as green (bottom). Colocalization of Sir3p with nucleolar fragments appears yellow in the merged image (top). The background shows an enlarged image of an NMT1 cell with the nucleolus intact. NMT1 encodes MyristoylCoA:protein N-myristoyltransferase, which covalently links myristate to proteins. nmt1-451D encodes an enzyme with a reduced affinity for myristoylCoA and nmt1-451D cells exhibit decreased resistance to nutrient deprivation. Deletion of the N-myristoylprotein Sip2p accelerates aging by increasing the activity of Snf1p, a serine/threonine kinase involved in regulating cellular responses to glucose starvation. (For details, see Ashrafi et al., p. 1872.)