DIFFERENTIAL EXPRESSION AND SEQUENCE-SPECIFIC INTERACTION OF KARYOPHERIN-ALPHA WITH NUCLEAR-LOCALIZATION SEQUENCES

The process of nuclear protein transport requires the interaction of s everal different proteins, either directly or indirectly with nuclear localization or targeting sequences (NLS). Recently, a number of karyo pherins alpha, or NLS-binding proteins, have been identified. We have found that the karyopherins hSRP1 and hSRP1 alpha are differentially e xpressed in various leukocyte cell lines and could be induced in norma l human peripheral blood lymphocytes, We show that the two karyopherin s bind with varied specificities in a sequence specific manner to diff erent NLSs and that the sequence specificity is modulated by other cyt osolic proteins. There was a correlation between binding of karyopheri ns cu to different NLSs and their ability to be imported into the nucl eus. Taken together, these data provide evidence for multiple levels o f control of the nuclear import process.