CLONING AND CHARACTERIZATION OF AN ADENOSINE KINASE FROM PHYSCOMITRELLA INVOLVED IN CYTOKININ METABOLISM

Adenosine kinase (adk) from the moss Physcomitrella patens (Hedw.) B.S .G. was cloned from a cDNA library by functional complementation of an Escherichia coil purine auxotrophic strain. The length of the entire cDNA clone was 1175 bp with an open reading frame coding for a protein with a predicted molecular weight of 37.3 kDa. Southern analysis indi cated the presence of a single adenosine kinase gene within the Physco mitrella genome. The deduced amino acid sequence had a 52% identity wi th the human adenosine kinase. The transfer of phosphate from ATP to a denosine resulting in AMP, as well as the phosphorylation of the cytok inin, isopentenyladenosine, to isopentenyladenosine monophosphate, was shown by in vitro enzyme assays using crude extracts from E. coil mut ants expressing the adk cDNA clone and from Physcomitrella chloronemal tissue. Results from in vivo feeding of chloronemal tissue with triti ated isopentenyladenosine suggest that adenosine kinase plays an impor tant role in the conversion of cytokinins towards their nucleotides in Physcomitrella.