A novel dual-specificity protein kinase targeted to the chloroplast in tobacco

The NtDSK1 cDNA encoding a novel chloroplast-targeted protein kinase was id entified in Nicotiana tabacum. It contains the kinase domain at the C-termi nus and a putative regulatory domain at the N-terminus. The recombinant NtD SK1 underwent autophosphorylation of serine, threonine, and tyrosine residu es, indicating that NtDSK1 encodes a functional dual-specificity protein ki nase. The NtDSK1-green fluorescent protein fusion protein was targeted to c hloroplasts. Furthermore, the NtDSK1 protein was immunodetected in chloropl ast fractions isolated from tobacco seedlings. The NtDSK1 mRNA expression w as developmentally regulated in different tissues, including anthers and ge rminating seeds, and strongly stimulated by gibberellin. The mRNA was rapid ly light responsive during seedling growth. NtDSK1 may play a role in a lig ht-regulated signaling process in tobacco. (C) 2001 Published by Elsevier S cience B.V. on behalf of the Federation of European Biochemical Societies.