Dysfunctionality of a tobacco mosaic virus movement protein mutant mimicking threonine 104 phosphorylation

1 Department of Virology and A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Vorobiovy Gory Moscow 119899, Russia 2 M. M. Shemyakin and Yu. A. Ovchinnikov Institut of Bioorganic Chemistry, Moscow, Russia 3 Joint Biotechnology Laboratory, Biocity, Turku, Finland 4 University of Helsinki, Institute of Biotechnology, Biocenter, Helsinki, Finland 5 Ludwig Institute of Cancer Research, Biomedical Center, Uppsala, Sweden Correspondence Joseph Atabekov atabekov{at}genebee.msu.su Replication of tobacco mosaic virus (TMV) is connected with endoplasmic reticulum (ER)-associated membranes at early stages of infection. This study reports that TMV movement protein (MP)-specific protein kinases (PKs) associated with the ER of tobacco were capable of phosphorylating Thr 104 in TMV MP. The MP-specific PKs with apparent molecular masses of about 45–50 kDa and 38 kDa were revealed by gel PK assays. Two types of mutations were introduced in TMV MP gene of wild-type TMV U1 genome to substitute Thr 104 by neutral Ala or by negatively charged Asp. Mutation of Thr 104 to Ala did not affect the size of necrotic lesions induced by the mutant virus in Nicotiana tabacum Xanthi nc. plants. Conversely, mutation of Thr to Asp mimicking Thr 104 phosphorylation strongly inhibited cell-to-cell movement. The possible role of Thr 104 phosphorylation in TMV MP function is discussed. Published ahead of print on 20 December 2002 as DOI 10.1099/vir.0.18972-0. Present address: Division of Experimental Clinical Chemistry, Lund University, Malmo University Hospital, Malmo, Sweden.