Comparison of crayfish serca isoforms from heart and tail muscle

The heart isoform of Sarco/Endoplasmic Reticulum Ca²⁺-ATPase (SERCA) from crayfish Procambarus clarkii has been identified by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The complete crayfish heart SERCA consists of 4495 bp with a 3060 bp open reading frame, coding for 1020 amino acids. This gene differs from the previously cloned tail muscle SERCA solely in its C-terminal amino acids. The last 9 amino acids of the tail muscle isoform are replaced by 27 hydrophobic amino acids in the heart isoform that have the potential of forming an additional transmembrane domain. The relationship between these SERCA isoforms in crayfish is similar to that of Artemia SERCA isoforms and two mammalian SERCA2 isoforms. The C-terminal extensions of these isoforms share their hydrophobic character but have no significant amino acid homology. Southern blot analysis suggested that the heart isoform and the tail muscle isoform are encoded by the same gene.