Primary structure of a gene-sized DNA encoding calmodulin from the hypotrichous ciliate Stylonychia lemnae.

We have isolated and characterized a gene-sized DNA encoding calmodulin (Clm) from macronuclear (MA) DNA of the hypotrichous ciliate, Stylonychia lemnae. The gene has 3500 copies per macronucleus. The length of the gene was deduced by agarose-gel electrophoresis of MA DNA and Southern blot analysis using a Clm cDNA probe from chicken. We then isolated the gene from a MA library. The overall length of the gene is 821 bp with a 450-bp intronless coding region. The deduced amino acid (aa) sequence of ciliate Clm has 149 aa and an M(r) of 16,819. Both ends of the cloned gene have the hypotrichous telomeric C4A4 repeat. The coding region is flanked by a 158-bp 5'-leader sequence and a 3'-trailer sequence of 213 bp. S1 analysis was used to locate the transcription start point (tsp) 49 bp upstream from the start codon. No common eukaryotic transcription signals were found upstream from the tsp. A second gene-sized DNA, detected by its cross-hybridization with the Clm DNA, predicts the existence of a second Ca(2+)-binding protein with only one Ca(2+)-binding site. It's function and biological significance is yet unknown.