CSM News Electronic Edition Volume 1, number 14 August 26, 1993 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 [129.105.233.50]. The next issue of the CSM News, Electronic Edition will be on Saturday, Sept. 18. Please continue to send abstracts! ---------- Abstracts ---------- An unusual catalytic subunit for the cAMP dependent protein kinase of Dictyostelium discoideum Christophe Anjard, Lilian Etchebehere*, Stephane Pinaud, Michel Veron* and Christophe D. Reymond. Universite de Lausanne, Institut d'Histologie et d'Embryologie, Rue du Bugnon 9, CH-1005, Lausanne, Switzerland. * Unite de Biochimie Cellulaire. CNRS-URA D1129, Institut Pasteur, 75724, Paris Cedex 15, France. BIOCHEMISTRY, In Press Summary The cAMP dependent protein kinase (cAPK) plays an essential role during differentiation and fruit morphogenenesis in Dictyostelium discoideum. The presence of an open reading frame on the gene pkaC (previously named either Dd PK2, or Dd PK3 by different groups) predicts a 73 kDa polypeptide with 54% similarity to the catalytic subunits of cAPKs from other organisms. Using anti-peptide antibodies, we show that the pkaC gene product, PkaC, is a 73 kDa polypeptide. Despite the fact that PkaC is about twice the size of its mammalian counterparts, it possesses all the properties required of a catalytic subunit. It is physically associated with the regulatory subunit and this association results in an inhibition of the catalytic activity which is reverted by cAMP. PkaC co-purifies with cAPK activity and an increased cAPK activity is observed in cells overexpressing PkaC. We conclude that PkaC is a catalytic subunit of the Dictyostelium discoideum cAPK and discuss the unusual features of this protein with the highest molecular weight of known cAPKs ---------------------------------------------------------------------- Prestalk cells in monolayer cultures exhibit two distinct modes of cellulose synthesis during stalk cell differentiation in Dictyostelium R.L. Blanton Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-3131, U.S.A. Development, in press. Abstract Stalk formation in Dictyostelium discoideum involves the synthesis of a stalk tube by the prestalk cell population and stalk cell walls by the individual prestalk cells. Cellulose is a major structural component of the stalk tube and stalk cell walls. The DIF-deficient strain HM44 was used to study the events of stalk formation in monolayer cultures. The induction of cellulose synthase activity was shown to require both DIF and cAMP. Microscopical observations of monolayer cultures using the cellulose-indicating fluorochrome Tinopal LPW demonstrated the presence in these cultures of two cellulose- containing materials: the stalk cell walls and an intercellular material found between cells and around cell clumps. The synthesis of intercellular material precedes that of stalk cell walls in induced cultures. Cells committed to stalk cell formation were delayed in doing so if they were switched to medium containing cAMP but no DIF. During this delay the cells synthesized large quantities of the intercellular material. The intercellular material was shown to be microfibrillar, was sensitive to cellulase, and labelled with a colloidal gold-conjugated cellulase. It is possible that the intercellular material represents a mode of cellulose synthesis related to that involved in stalk tube formation. If so, that mode would be favored by DIF and cAMP in combination, whereas the cellulose synthesis involved in stalk cell wall formation would be DIF-dependent but delayed or repressed by cAMP. ------------------------------------------------------------------- [[END CSM-News, volume 1, number 14]]