Bipartite signal sequence mediates nuclear translocation of the plant potyviral NIa protein.

Abstract

The Nla protein of certain plant potyviruses localizes to the nucleus of infected cells. Previous studies have shown that linkage of Nla to reporter protein @-glucuronidase (GUS) is sufficient to direct GUS to the nucleus in transfected protoplasts and in cells of transgenic plants. In this study, we mapped sequences in Nla that confer karyophilic properties. A quantitative transport assay using transfected protoplasts, as well as an in situ localization technique using epidermal cells from transgenic plants, were employed. Two domains within Nla, one between amino acid residues 1 to 11 (signal domain I) and the other between residues 43 to 72 (signal domain ll), were found to function additively for efficient localization of fusion proteins to the nucleus, although either region independently could facilitate a low leve1 of translocation. Like signals from animal cells, both nuclear transport domains of Nla contain a high concentration of basic (arginine and lysine) residues. Nuclear transport signal domain II overlaps or is very near TyP, which is the residue that mediates covalent attachment of a subset of Nla molecules to the 5' terminus of viral RNA within infected cells. The nature of the Nla nuclear transport signal and the possibility for regulation of Nla translocation are discussed.

Nuclear localization signal(s) required for nuclear targeting of the maize regulatory protein Opaque-2.

“…However, in some constructs, the first half may be recognized by the import machinery ( l abl e 4). Other studies show that the first half of bipartite NLSs may be a more efficient targeting signal than the second half (Carrington et al, 1991;Howard et al, 1992;Xia et al, 1992).…”

“…Figure 6C shows the amino acid sequences of NLSs that have redirected GUS fusion proteins to the plant cell nucleus. These bipartite NLSs are found in the Nla protein from potyvirus (Carrington et al, 1991) and in the VirD2 and VirE2 encoded on the Agrobacterium Ti plasmid (Howard et al, 1992;Citovsky et al, 1992, respectively). Dingwall and Laskey (1991) suggest that the bipartite NLS is the most prevalent NLS in nonplant proteins.…”

“…Most of these reports have concentrated on proteins from vira1 and bacterial phytopathogens. Carrington et al (1991) identify a bipartite NLS in the potyviral protein Nla. Bipartite NLSs are also present in the Agrobacterium proteins VirD2 (Howard et al, 1992) and VirE2 .…”

Nuclear Targeting in Plants

“…Furthermore, experimental evidence indicates the existence of receptors and other cellular factors that mediate nuclear transport. Nuclear transport, although extensively studied in animal and lower eukaryotic systems (3, 20), has only recently been addressed in higher plants (1,2,5,7,8,15,(24)(25)(26).This attention to protein and nucleic acid transport into the nucleus in plants was stimulated not only by a need to understand basic cell biology, but also by the desire to modulate or regulate the expression of genes via genetic engineering.The nucleus (Fig. 1) is surrounded by the nuclear envelope, which includes the inner and outer nuclear membranes and, between them, the perinuclear space.…”

“…Furthermore, experimental evidence indicates the existence of receptors and other cellular factors that mediate nuclear transport. Nuclear transport, although extensively studied in animal and lower eukaryotic systems (3, 20), has only recently been addressed in higher plants (1,2,5,7,8,15,(24)(25)(26).…”