Cell Biology

(The Scientist, Vol:4, #22, pg. 20, November 12, 1990) (Copyright, The Scientist, Inc.) -------- S. Shenoy, J.-K. Choi, S. Bagrodia, T.D. Copeland, J.L. Maller, D. Shalloway, "Purified maturation promoting factor phosphorylates pp60c-src at the sites phosphorylated during fibroblast mitosis," Cell, 57, 763-74, 2 June 1989. Suresh Shenoy (Cornell University, Ithaca, N.Y.): "A lot of credit for this work belongs to Jung-Kap Choi (Chonnam National University, Korea), who mapped the sites of mitosis-specific phosphorylation in pp60c-src. This paper has been receiving many citations because of two illustrations that were conceived by James Maller and David Shalloway (Pennsylvania State University, University Park). In the first sketch, we demonstrated that the serine and threonine residues that were phosphorylated during mitosis resided in consensus sequences recognized by p34cdc2. In the second, we depicted a potential cascade of kinases that was initiated by p34cdc2 and involved pp60c-src. This paper, along with a similar one from the labs of David O. Morgan, Joshua M. Kaplan, J. Michael Bishop, and Harold E. Varmus at the University of California, San Francisco (Cell, 57:775-786, 1989) and another by Isaac Chack- alaparampil and David Shalloway (Cell, 52:801-810, 1988), have opened a field of research that is investigating the interaction of proto-oncoproteins and p34cdc2 during mitosis. It was absolutely thrilling to be involved in the experiments described in this paper. The desire for another high promises to keep me at the bench for a long time." S. Moreno, J. Hayles, P. Nurse, "Regulation of p34cdc2 protein kinase during mitosis," Cell, 58, 361-72, 28 July 1989. Sergio Moreno (Imperial Cancer Research Fund, University of Oxford, England): "The last couple of years have been important for understanding regulation of the cell cycle, especially entry into mitosis. Efforts made by many different groups working in yeast, Drosophila, frogs, and mammalian cell cultures have led to the idea that M-phase is initiated by the activation of the universal regulator cdc2M^>+ protein kinase. "In this paper, we confirmed in the fission yeast that the activity of p34cdc2 protein kinase oscillates during the cell cycle, peaking at the time of the onset of mitosis. Activation of this protein kinase requires the positive element cdc25+, a protein that changes in level during the cell cycle accumulating in G2 and provides the link between completion of S-phase and initiation of mitosis. We also shows that the cyclin homologue, cdc13+, is necessary for activation of the kinase and confirmed that this protein is destroyed at anaphase. A fourth protein, suc1+, appears to be required for completion of mitosis. In conclusion, we showed that entry into M-phase in fission yeast is similar to that in higher eukaryotes. For fission yeast, however, we have all the genetic elements available. There- fore, through a combination of genetics and biochemistry, we were able to elucidate the regulation of the activation of this universal protein kinase." K.L. Gould. P. Nurse, "Tyrosine phosphorylation of the fission yeast cdc2+ protein kinase regulates entry into mitosis," Nature, 342, 39-45, 2 November 1989. Kathleen L. Gould (Imperial Cancer Research Fund, University of Oxford, England): "The p34cdc2 protein kinase regulates entry into mitosis in all eukaryotes. Many investigators have been interested in determining how its activity is regulated in biochemical detail. Several reports have found a correlation between dephosphorylation and activation of p34cdc2 protein kinase activity. Since we were using genetically tractable fission yeast for our studies, we were able to demonstrate conclusively that tyrosine dephosphorylation of a residue within the presumptive ATP-binding domain is the key element in controlling the timing of p34cdc2 activation and entry into mitosis in this organism. This paper also contained the first description of tyrosine phosphorylation of a known protein in yeast. As a consequence, it has stimulated interest in identifying and characterizing protein-tyrosine kinases and phosphatases from both budding and fission yeasts." (The Scientist, Vol:4, Issue 22 pg 20, ) (Copyright, The Scientist, Inc.) WE WELCOME YOUR OPINION. IF YOU WOULD LIKE TO COMMENT ON THIS STORY, PLEASE WRITE TO US AT EITHER ONE OF THE FOLLOWING ADDRESSES: garfield@aurora.cis.upenn.edu 71764.2561@compuserve.com The Scientist, 3600 Market Street, Suite 450, Philadelphia, PA 19104 U.S.A.

Cell Biology

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