Fig. 4. Northern blot analysis of the distribution of the two crayfish SERCA isoforms (from heart and axial muscle) in intermoult tissues. Messenger RNAs from eggs, heart muscle and axial abdominal muscle were hybridized with the following probes: (A) the 426 bp fragment corresponding to crayfish nucleotides 2086-2546 in both heart and axial muscle SERCA; (B) the 723 bp XbaI—poly(A) tail fragment of the putative heart SERCA; (C) the 515 bp XhoI—poly(A) tail fragment of the putative muscle SERCA. The positions of marker nucleotides are shown at the left.