Plant Molecular Biology 23:543-551, 1993. © 1993 Kluwer Academic Publishers. Printed in Belgium. 543 Isolation and characterization of a tobacco cDNA clone encoding a putative MAP kinase Cathal Wilson 1, Norbert Eller ~, Anton Gartner 2, Oscar Vicente 1,. and Erwin Heberle-Bors 1 l Institute of Microbiology and Genetics, University of Vienna, Vienna Biocenter, Dr Bohr-Gasse 9, A-1030 Vienna, Austria (* author for correspondence); 2Institute of Molecular Pathology, Vienna Biocenter, Dr Bohr-Gasse 7, A-I030 Vienna, Austria Received 11 February; accepted in revised form 27 July 1993 Key words: Cell cycle, MAP kinases, Nicotiana tabacum, pollen development, pollen embryogenesis, starvation Abstract We have isolated and sequenced a MAP (mitogen-activated protein) kinase-type cDNA from a tobacco (Nicotiana tabacum L.) cell suspension cDNA library by screening with a PCR fragment amplified from the same library with oligonucleotide primers corresponding to two sequences conserved in yeast and animal MAP kinases. The tobacco sequence, ntf3, shows 45-54~o identity to various members of the MAP kinase family at the protein level. Northern experiments showed that ntf3 is expressed in all tobacco tissues tested, including pollen isolated at different developmental stages. Southern analysis indicated that, as in other organisms, there is a family of MAP kinase genes in tobacco. In complementary tests, ntf3 could not substitute the yeast MAP kinase genes fus3 and kssl. Introduction Cell proliferation and differentiation can be in- duced by extracellular signals which operate through transduction pathways from receptor binding to downstream target molecules via phos- phorylation cascades. MAP kinases, also known as extracellular signal-regulated kinases (ERKs), are a family of serine/threonine protein kinases which have been shown to be intermediates in a variety of signal transduction pathways, induced by different extracellular stimuli [27]. The MAP kinase gene family has been highly conserved during evolution, with members found in such diverse organisms as mammals, Xenopus and yeast [20]. They have been grouped together on the basis of sequence homology as well as by chromatographic and immunological criteria. Treatment of quiescent mammalian cells (cells in GO) with an array of mitogenic agents, includ- ing insulin, nerve growth factor, epidermal growth factor or phorbol esters ([5] and references therein) induces reactivation of the cell cycle and cell proliferation. The transition G0/G1 is medi- The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X69971 (N. tabacum NTF3 mRNA).