Screening of Genes Encoding Nuclear Localization Signal in a Mouse Embryonic cDNA Library.

A genetic screening system was established previously for the cloning of gene fragments encoding nuclear localization signals (NLS). In the current study, the system was improved and its ability to distinguish nuclear and cytoplasm-localized proteins was verified by inserting a known NLS-encoding gene. A mouse 10.5-d pc embryonic cDNA library was then inserted into the cloning site of the screening vector and 22 out of 10(4) clones were shown to be positive after screening using the system. The cDNA inserts of some of these clones were sequenced, and typical and untypical NLS were identified. The nuclear localizing activity of the cDNA inserts was further verified using the GFP fusion protein system. So, the system is useful in the cDNA library screening of genes encoding NLS-bearing proteins.