Structural dynamics of F-actin: I. Changes in the C terminus.

The biochemical properties of G-actin, and the kinetics of polymerization of G-actin into F-actin, are dependent upon whether Mg2+ or Ca2+ is bound at the high-affinity metal-binding site in actin. Three-dimensional reconstructions from electron micrographs show that a bridge of density, that we interpret as arising from a major shift of the C terminus, exists between the two strands of the filament in Ca(2+)-actin that is absent in Mg(2+)-actin. This bridge is also absent in models of F-actin built from an atomic structure of G-Ca(2+)-actin.

Immediate differentiation of ganglion cells following mitosis in the developing retina.

The aim of this study is to gain insight into the time during the life history of a retinal neuron that it becomes committed to a particular phenotype. At this point, it is not possible to identify the time of commitment, but the time that differentiation begins can be identified. Bromodeoxyuridine labeling coupled with immunohistochemistry with a ganglion cell-specific antibody was used to fix the time of the beginning of ganglion cell differentiation relative to the time of mitosis in the developing chick retina.