Microsequencing of myosins for PCR primer design.

Their large size and their relative resistance to proteolytic cleavage (1) make myosins particularly difficult substrates for the acquisition of their peptide sequences by standard protocols. For this reason, instead of identifying myosins first according to their biochemical activity and then obtaining their sequences, PCR and other DNA-based techniques exploiting the highly conserved sequences in the amino end, the “head” domain, have been used to find new myosins (2–5). However, such identification of myosins by sequence leaves open the question of their function. If peptide sequence could be obtained from myosin proteins whose biochemical behavior was known, then the gap between function and sequence could be bridged. We describe here a method that enabled us to acquire peptide sequences of semi-purified myosins (6).