Phosphorylated and dephosphorylated myosin light chains of Drosophila fly and larva

Abstract

1. 1. The present study confirmed that light chains of Drosophila adult fibrillar (flight) muscle myosin consist of Lf1, Lf2, Lf2′ and Lf3, and tubular muscle myosin light chains contain Lt1, Lt2 Lt2′ and lt3, as revealed by two-dimensional (isoelectric focusing and SDS-gel electrophoresis) gel electrophoresis. 2. 2. larva myosin light chains were of all the tubular type. However, it was found that Ltl and Lt2′ are produced by phosphorylation of Lt2, and Lf1 is produced by phosphorylation of Lf2′. 3. 3. Injection of radioactive phosphate into Drosophila fly resulted in phosphorylations of Lf1 and Lt1. When larva or late pupa myosin was incubated with myosin light chain kinase from chicken gizzard or adult flies, phosphorylation of Lt1, Lf2′ and Lt2′ occurred. Drosophila myosin light chain kinase phosphorylated Lf1 in addition to Lt1 and L2′ ( Lf2′ + Lt2′) of adult myosin. 4. 4. Dephosphorylation of adult myosin by potato acid and calf intestine alkaline phosphatases led to the shift of Lf1 (34,000), Lt1 (31,000) and L2′ ( Lf2′ + Lt2′) (30,000 to L2 ( Lf2 + Lt2) positions (30,000). 5. 5. Peptide mapping analyses revealed that larva Lt1, Lt2′, Lt2 and adult Lt1 were all the same; therefore, it is thought that a single species of Lt2 specific to the tubular type of myosin and its phosphorylated isoforms (Lt1, Lt2′) exist. 6. 6. The peptide map of Lf1 was slightly different from that of Lt1, but very similar to that of L2′ in adult myosin. L2 and L2′ of adult myosin showed very similar peptide maps, but there were several different peptide fragments. 7. 7. There were a number of peptides common to L1 (Lf1, Lt1) and L2 (Lf2′, Lt2′, Lf2 and Lt2) but not to L3 (Lf3, Lt3). 8. 8. It is concluded that Lf2′ ( = Lf1), Lf2 (fibrillar muscle) and Lt2 (= Lt1 = Lt2′) (tubular muscle) are the regulatory light chains of Drosophila myosin and that Lf3 (fibrillar) and Lt3 (tubular) are the essential light chains in view of the present findings as well as of the reported results of the gene analyses.