Nuclear localization refers to the process of directing a protein or molecule to the nucleus of a cell. This process is critical for a wide range of cellular functions such as gene expression, DNA replication, and cell division. Proteins that are needed in the nucleus typically have a specific nuclear localization signal (NLS) sequence that allows them to be recognized and transported into the nucleus by nuclear transport machinery. Understanding nuclear localization is important for studying various cellular processes and diseases, as disruptions in this process can lead to abnormal cell function and potentially contribute to the development of diseases such as cancer. Researchers use a variety of techniques such as fluorescent labeling and microscopy to study nuclear localization in both normal and diseased cells.