Sequence motif in control regions of the H+/K+ ATPase alpha and beta subunit genes recognized by gastric specific nuclear protein(s).

A nuclear protein(s) from rat or pig stomach recognized a conserved sequence in the 5'-upstream regions of the rat and human H+/K(+)-ATPase alpha subunit genes. A gel retardation assay suggested that part of the binding site was located in the TAATCAGCTG sequence. No nuclear proteins capable of the binding could be detected in other tissues of rat (liver, brain, kidney, spleen and lung) or pig liver. The sequence motif (GATAGC) located 5'-upstream of the beta-subunit gene also seemed to be recognized by the same protein, because the binding of nuclear protein to the sequence motifs in the alpha and beta subunits was mutually competitive. Considering the sense-strand sequence of the binding motif in the alpha-subunit gene, we conclude that (G/C)PuPu(G/C)NGAT(A/T)PuPy is a core sequence motif for the gastric specific DNA binding protein (PCSF, parietal cell specific factor).     

The NPI-1/NPI-3 (karyopherin alpha) binding site on the influenza a virus nucleoprotein NP is a nonconventional nuclear localization signal.

Two cellular proteins, NPI-1 and NPI-3, were previously identified through their interaction with the influenza virus nucleoprotein (NP) by using the yeast two-hybrid system. These proteins were then shown to act as general transport factors (karyopherin alpha) and nuclear pore-docking proteins to facilitate the transport of the NP and of viral RNA into the nucleus. The yeast two-hybrid assay has now been used to identify the specific domains on the NP that bind to the NPI proteins. Mutational analysis including alanine scanning identified the motifs SxGTKRSYxxM and TKRSxxxM, which are required for binding to NPI-1 and NPI-3, respectively. These sequences were shown to possess nuclear localization signal (NLS) activity following expression of fusion proteins in HeLa cells. These sequences represent a novel nonconventional NLS motif. Another NLS activity not mediated by the NPI binding sites is associated with noncontiguous sequences in the NP.