Identification of a Sequence in Influenza Virus Nucleoprotein Which Specifies Nuclear Accumulation in Xenopus Oocytes

Abstract

It has been known for a long time that a subclass of cellular proteins accumulate in the nucleus of the interphase eukaryotic cell. Experimental interest has focussed on two aspects of the accumulation process. First, studies have been directed at understanding the cellular mechanisms which underlie the observed nuclear accumulation. The selectivity of the uptake process (Bonner, 1975a,b; De Robertis et al., 1973; De Robertis and Black, 1981; Dabauvalle and Franke, 1982) led to the proposal that the accumulation is controlled by a signal contained within the mature molecular structure of the protein and two types of approach have been used to identify and localize such a karyophilic signal. The first is exemplified by the work of Dingwall et al. (1982), who used partial proteolysis of nucleoplasmin, the most abundant nuclear protein in Xenopus oocytes (Mills et al., 1980; Krohne and Franke, 1980), to produce two fragments, only one of which retained the ability to migrate into and accumulate in the oocyte nucleus. The second approach involves the use of DNA recombinant methodology to construct genes in which various regions have been deleted or altered. In this way Kalderon et al. (1984) have identified a region of the SV40 large T antigen necessary for its accumulation in the nuclei of transformed Rat-1 cells. A further modification of this approach involves the construction and expression of chimeric genes containing various regions of a nuclear protein fused to a cytosolic protein. In this way Hall et al. (1984) have identified an amino-terminal region of the yeast protein a2, which can transport bacterial ß-galactosidase into the yeast cell nucleus.