Abstract
Transcription factor proteins function in the nucleus to regulate gene expression. Many transcription factors are critical regulators of tumor progression. Conversely, many oncogenic and tumor suppressor proteins are transcription factors or other types of nuclear proteins. Because of their critical physiological and pathological roles, these tumor regulators are tightly regulated not only in the protein expression but also in their subcellular localization. This chapter is focused on experimental strategies and method details for the identification and characterization of nuclear localization signal sequences for nuclear proteins using the Krüppel-like transcription factor 8 as an example.