CSM News Electronic Edition Volume 3, number 20 December 31, 1994 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web through www.nwu.edu. ======================== Happy New Year To All! ======================== =========== Abstracts =========== Characterization of FP21, a Cytosolic Glycoprotein from Dictyostelium. E. Kozarov, H. van der Wel, M. Field, M. Gritzali, R. D. Brown, Jr. and C. M. West. Dept. of Anatomy & Cell Biology, College of Medicine, and Food Science and Human Nutrition Dept., IFAS, Univ. of Florida, Gainesville, FL 32610-0235 USA J. Biol. Chem., in press FP21 is a glycoprotein which, when tracked by radioactivity in its fucosyl moiety, was previously detected in the cytosol of Dictyostelium cells after cell fractionation. This compartmentalization is confirmed by SDS-PAGE/Western blotting of cell fractions using three different antibodies. Though a substantial fraction of FP21 is also detected in the particulate fraction using these new antibodies, particulate FP21 is released by disrupting protein-protein interactions, but not membrane disruption. Since purified FP21 is susceptible to aggregation, and purified nuclei do not contain FP21, particulate FP21 is also part of the cytosol. Additional compositional and structural information provides strong evidence that FP21 does not at any time traverse the rough endoplasmic reticulum. First, cDNAs spanning the entire coding region of the FP21 gene predict no hydrophobic motifs expected to promote membrane insertion, but do predict an N-terminal coiled-coil domain which could explain aggregation. Second, monosaccharide composition analysis of the predominant glycoform of FP21 yields 2 mol galactose, 1 mol xylose, and 1 mol fucose per mol polypeptide; FP21 from a fucosylation-defective mutant contains 1 additional mol xylose in place of fucose. Thus the N-glycosylation sequon present in FP21 is not utilized by oligosaccharyl transferase, which resides in the rough endoplasmic reticulum. These findings indicate that nascent FP21 remains in the cytosol after synthesis, and is therefore glycosylated by unusual cytosolic xylosyl, galactosyl and fucosyl transferases. ---------------------------------------------------------------------- The Differentiation of a Cell Sorting Mutant of Dictyostelium discoideum. T. A. Ferguson, J. Vozenilek and C. M. West. Dept. of Anatomy and Cell Biology, Univ. of Florida College of Medicine, Gainesville, FL 32610-0235 USA Dev., Growth & Differen., in press As a result of transfecting Dictyostelium discoideum with an actin 6/lacZ fusion transgene, strain HW80 was created which expresses the b-galactosidase gene product uniformly throughout development. When mixed with an excess of unmarked wild-type cells, however, HW80 cells selectively migrate to the positions of anterior-like cells surrounding the prespore cell mass, and differentiate as if they were anterior-like cells. As the proportion of HW80 cells is increased, they also sort to positions adjacent to anterior-like cells and some differentiate as prespore cells. Thus sorting of HW80 cells toward the opposite ends of the prespore cell zone supersedes how they differentiate, suggesting that position influences whether cells differentiate as anterior-like or prespore cells. --------------------------------------------------------------------- [End CSM News, volume 3 number 20]