title: Localization of the rat myosin I molecules myr 1 and myr 2 and in vivo targeting of their tail domains.
abstract: Myr 1 is a widely distributed mammalian myosin I molecule related to brush border myosin 1. A second widely distributed myosin I molecule similar to myr 1 and brush border myosin I, called myr 2, has now been identified. Specific antibodies and expression of epitope-tagged molecules were used to determine the subcellular localization of myr 1 and myr 2 in NRK cells. Myr 1 was detected at the plasma membrane and was particularly enriched in cell protrusions like lamellipodia, membrane ruffles and filopodia. In dividing cells myr 1 localized to the cleavage furrow. Myr 2 was localized in a discrete punctate pattern in resting cells and in cells undergoing cytokinesis. In subcellular fractionation experiments myr 1 and myr 2 were both partly soluble and partly associated with smooth membranes of medium density. The tail domains of myosin I molecules have been proposed to interact with a receptor and thereby determine the subcellular localization. To test this hypothesis we expressed the tail domains of myr 1 and myr 2 that lack the F-actin-binding myosin head domain in NRK cells. These tail domains also partly copurified with smooth membranes of medium density and immunolocalized similar to the respective endogenous myosin I; however, they exhibited a lower affinity for membranes and an increased diffuse cytosolic localization. These results suggest that the tail domains of myr 1 and myr 2 are sufficient for subcellular targeting but that their head domains also contribute significantly to maintaining a proper subcellular localization.
authors.affiliation: Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, Tubingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Ruppert
authors.forename: J
authors.initials: J
authors.lastname: Godel
authors.forename: R T
authors.initials: RT
authors.lastname: Müller
authors.forename: R
authors.initials: R
authors.lastname: Kroschewski
authors.forename: J
authors.initials: J
authors.lastname: Reinhard
authors.forename: M
authors.initials: M
authors.lastname: Bähler
mesh_terms: D000199:Actins / Q000032:analysis; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D000939:Epitopes; D019084:Fluorescent Antibody Technique, Indirect; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D024461:Myosin Type I; D009218:Myosins / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis; D012672:Semliki forest virus / Q000235:genetics; D013347:Subcellular Fractions / Q000737:chemistry*
chemical_list: D000199:Actins; D000939:Epitopes; C104297:Myo1b protein, rat; D011994:Recombinant Proteins; D024461:Myosin Type I; D009218:Myosins