Tyrosine phosphorylation accompanying the cellularization of the syncytial blastoderm of Drosophila.

At an early stage in embryogenesis, the Drosophila blastoderm is a syncytium in which approximately 6000 nuclei align under the plasma membrane. During the interphase of nuclear cycle 14, a wave of membrane formation descends from the blastoderm surface to enclose each nucleus in an intact cell membrane. We show by immunofluorescence microscopy that the membrane-formation process is closely accompanied in space and time by a wave of tyrosine phosphorylation, suggesting that one or more tyrosine kinases and phosphatases are active in the process.

Escherichia coli iron superoxide dismutase targeted to the mitochondria of yeast cells protects the cells against oxidative stress.

A gene encoding a fusion protein consisting of Escherichia coli iron superoxide dismutase (FeSOD) with the mitochondrial targeting presequence of yeast manganese superoxide dismutase (MnSOD) was cloned and expressed in E. coli and in Saccharomyces cerevisiae DL1Mn- yeast cells deficient in MnSOD. In the yeast cells the fusion protein was imported into the mitochondrial matrix. However, the presequence was not cleaved. In a control set of experiments, the E. coli FeSOD gene without the yeast MnSOD leader sequence was also cloned and expressed in S. cerevisiae DL1Mn- cells. In this case the FeSOD was located in the cytosol and was not imported into the mitochondrial matrix. E. coli FeSOD, with and without the yeast MnSOD presequence, proved to be active in yeast, but, whereas the FeSOD targeted to the mitochondria of yeast cells deficient in MnSOD protected the cells from the toxic effects of oxidative stress, FeSOD without the yeast MnSOD presequence did not protect the yeast cells deficient in MnSOD against oxidative stress.