Nla and Nlb of peanut stripe potyvirus are present in the nucleus of infected cells, but do not form inclusions.

We investigated, by immunological and gene-fusion methods, whether the failure of peanut stripe potyvirus (PStV)-encoded nuclear inclusion proteins a (Nla) and b (Nlb) to form nuclear inclusions is due to the lack of their in vivo accumulation or the inability of one or both proteins to be transported into the nucleus Nla domains (Nla-VPg and Nla-proteinase), full-length Nlb, and full-length cylindrical inclusion (CI) protein of PStV were cloned, expressed in Escherichia coli, and used for antisera production. Immunoblot analysis of accumulation of Nla, Nlb, and CI in time course experiments revealed that they accumulated to similar levels in PStV-infected Nicotiana benthamiana. In immunocytochemical studies with electron microscopy, antiserum against Nla-VPg, Nla-Pro, and Nlb specifically labeled Nla and Nlb proteins throughout the nuclei of PStV-infected cells, in the absence of nuclear inclusions. Translational fusions were made between Nla and Nlb to either the green fluorescence protein or the beta-glucuronidase in vectors for transient gene expression or stable expression in transgenic plants respectively. Fusion proteins containing Nla accumulated in the nucleus, whereas fusion proteins containing Nlb accumulated in a punctate pattern in the cytoplasm. These data indicate that at least Nla possesses a nuclear localization signal.