GAP45 phosphorylation is involved in assembly of the myosin XIV motor complex. Parasites transiently expressing mycGAP45 (wt), mycGAP45(Ser163Ala), mycGAP45(Ser163Glu), mycGAP45(Ser167Ala), mycGAP45(Ser167Glu), mycGAP45(Ser163Ala, Ser167Ala), and mycGAP45(Ser163Glu, Ser167Glu) were immunoprecipitated with a monoclonal antibody to the myc epitope. Immunoprecipitates were analyzed by SDS-PAGE and immunoblotting with monospecific rabbit antisera to MyoA, GAP50, GAP45, and MLC1.