In contrast to the slow rate of depolymerization of pure actin in vitro, populations of actin filaments in vivo turn over rapidly. Therefore, the rate of actin depolymerization must be accelerated by one or more factors in the cell. Since the actin dynamics in Listeria monocytogenes tails bear many similarities to those in the lamellipodia of moving cells, we have used Listeria as a model syste...

Bone morphogenetic protein 1 (BMP1) is a metalloprotease that ventralises dorsal mesoderm when overexpressed in early Xenopus embryos. Here we show that Xenopus BMP1 blocks the dorsalising activity of chordin, but not noggin or DeltaxBMPR, when coexpressed in the ventral marginal zone and degrades chordin protein in vitro. We also show that a dominant-negative mutation for XBMP1 (dnBMP1) dorsal...

The calcium-binding protein, calmodulin, has been purified from Xenopus laevis oocytes. This 18,500-dalton protein, pl 4.3, has two high-affinity calcium-binding sites per mole protein having a dissociation constant of 2.8 x 10(-6) M. Full-grown Xenopus oocytes, arrested in late G2 of the meiotic cell cycle, resumed meiosis when microinjected with 60-80 ng (3-4 pmol) of calmodulin in the form o...

Xenopus embryos provide a rich source of pluripotent cells that can be differentiated into functional organs. Since the molecular principles of vertebrate organogenesis appear to be conserved between Xenopus and mammals, this system can provide useful guidelines for the directional manipulation of human embryonic stem cells. Pluripotent Xenopus cells can be easily isolated from the animal pole ...

The origin recognition complex (ORC) binds to origins of replication in budding yeast. We have cloned a Xenopus homolog of the largest ORC polypeptide (XORC1). Immunodepletion of XOrc1 from Xenopus egg extracts blocks the initiation of DNA replication. We have purified Xenopus ORC, consisting of a protein complex similar to yeast ORC. In Xenopus egg extracts, ORC associates with chromatin throu...