ISOLATION AND CHARACTERIZATION OF 2 CDNAS THAT ENCODE FOR CALMODULIN-BINDING PROTEINS FROM CORN ROOT-TIPS

A corn root tip cDNA expression library was screened with S-35-labeled calmodulin to isolate cDNAs that code for calmodulin-binding proteins (CBP). Several positive clones that bind to S-35-calmodulin were isolated. Two CBP clones (CBP-1 and CBP-5) that bind to S-35-labeled calmodulin as well as biotinylated calmodulin were sequenced and characterized. Comparison of the deduced amino acid sequence of both the clones showed one hundred percent conservation of a 34-amino acid stretch at their carboxy-terminal end. Whereas, less homology was observed in other regions of amino acid sequence. The highly conserved 34-amino acid stretch contained a putative calmodulin-binding domain, a basic amphiphilic alpha helix. The nucleotide and deduced amino acid sequence of both the clones did not show homology with any of the sequences in the nucleic acid and protein data bases. Northern analysis with both CBP-1 and CBP-5 clones indicated that the corresponding genes are expressed in different parts of the root although there was a difference in the extent of expression. Wind induced the expression of CBP-5, but it did not have any effect on CBP-1 mRNA level. Southern analysis indicated that CBP-1 and CBP-5 are coded, most likely, by one or two genes.