Characterisation of a tripartite nuclear localisation sequence in the regulatory protein Lys14 of Saccharomyces cerevisiae.

The Lys14 regulatory protein of Saccharomyces cerevisiae activates the expression of the LYS genes involved in the lysine biosynthetic pathway. Studies with a fused Lys14-green fluorescent protein reveal that Lys14p is localised to the nucleus, even under growth conditions leading to the absence of LYS gene expression. Lys14p nuclear localisation is mediated by a tripartite sequence made up of three short basic motifs located on the C-terminal side of the Zn cluster domain of Lys14p. Substitution of basic residues by alanines in any of the three motifs partially prevents the nuclear import of the protein. Simultaneous mutations in the three basic domains are required to completely abolish the entry into the nucleus and to impair the Lys14 function.