核定位串行（英语：nuclear localization signal，或称为核定位信号,英语：nuclear localization sequence，缩写NLS）是一段氨基酸串行，作为细胞核通过核运输进入细胞核的标签。一般来说，核定位信号通常由一段或几小段氨基酸串行组成，通常都为带正电荷赖氨酸或精氨酸，且暴露于蛋白表面。不同的入核蛋白可能使用相同的核定位信号。核定位串行的功能与核输出串行相反，后者将蛋白送出细胞核。

A nuclear localization signal or sequence (NLS) is an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal, which targets proteins out of the nucleus.