Cloning and characterization of an apple (Malus domestica (L.) Borkh) cDNA encoding a calmodulin-binding protein domain similar to the calmodulin-binding region of type II mammalian Ca2+/calmodulin-dependent protein kinase

Abstract A cDNA expression library constructed in the λgt11 vector with mRNA isolated from in vitro grown apple plantlets was screened with 125 I-labeled calmodulin as a probe. One recombinant clone, λCBI, produces a fusion protein that binds calmodulin in a Ca 2+ -dependent manner. This clone contains a cDNA insert of 378 base pairs encoding a truncated polypeptide of 126 amino acids that exhibits sequence similarities to the subunits of the mammalian Ca 2+ /calmodulin-dependent protein kinase II. Northern blot hybridization analysis indicates that this insert hybridizes with a mRNA species of about 2100 nucleotides. Genomic DNA Southern analysis suggests that this mRNA is encoded by a single- or low-copy number gene in apple. Furthermore, CBI-related sequences were detected in genomic DNA from other plant species using λCBI insert as a probe. Our results demonstrate that plant cDNA expression libraries can be successfully screened for genes encoding proteins that bind calmodulin in the presence of Ca 2+ .