Cytoskeletons from a mutant of Dictyostelium discoideum with flattened cells.

Development of a mutant of Dictyostelium discoideum, HG403, is described whose cells spread strongly on a substratum. Although the mutant cells were less clearly polarized into the front and rear ends, and usually less extensively elongated than wild-type cells, their aggregation pattern was only slightly less regular. Cells of the mutant responded well to cyclic AMP by chemotaxis, although their capability of stabilizing cell shape and maintaining dominance of a single moving front appeared to be reduced.

Fractionation and characterization of two molecular variants of myosin from adult human atrium.

Monoclonal antibodies (MAb) to myosin heavy chains were prepared from one adult human ventricular myocardium. Several of these MAb reacted by indirect immunofluorescence in a heterogenous way on cryostat transverse sections of fibers from human atrial myocardium, suggesting the presence of different forms of myosin within the human atrium and prompting the further use of the MAb to attempt to fractionate preparations of native atrial myosins. Two molecular variants of human atrial myosins or myosin fragments were thus separated by immunoaffinity chromatography performed with one antiventricular myosin MAb.

Incomplete contact site A glycoprotein in HL220, a modB mutant of Dictyostelium discoideum.

HL220, a modB mutant that lacks a modification of certain membrane proteins of Dictyostelium discoideum, has been shown to aggregate and to form EDTA-stable intercellular contacts typical of aggregating wild-type cells. A developmentally regulated glycoprotein of 80 X 10(3) apparent molecular weight has been identified as a target site of adhesion-blocking Fab and thought to be involved in EDTA-stable cell contact formation (Müller & Gerisch, 1978). In the HL220 mutant this glycoprotein is no longer recognized by a modB-specific antibody.

Localization of two phosphorylation sites adjacent to a region important for polymerization on the tail of Dictyostelium myosin.

Phosphorylation of the myosin heavy chains of Dictyostelium discoideum is known to be inhibited following chemotactic stimulation of the cells. Effects of dephosphorylation on the assembly of myosin and on its actin-activated ATPase activity raised the question of where the phosphorylated sites are located with respect to sites responsible for polymerization and actin binding. Using seven monoclonal antibodies the binding sites of which were mapped in the electron microscope, two phosphorylation sites, i.

Flagella and motility behaviour of square bacteria.

Square bacteria are shown to have right-handed helical (RH) flagella. They swim forward by clockwise (CW), and backwards by counterclockwise (CCW) rotation of their flagella. They are propelled by several or single filaments arising at several or single points on the cell surface.