dictyNews Electronic Edition Volume 39, number 4 February 8, 2013 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= A Rare Combination of Ribonucleotide Reductases in the Social Amoeba Dictyostelium discoideum Mikael Crona, Lotta Avesson, Margareta Sahlin, Daniel Lundin, Andrea Hinas, Ralph Klose, Fredrik Soderbom, and Britt-Marie Sjoberg Journal of Biological Chemistry, in press Ribonucleotide reductases (RNRs) catalyze the only pathway for de novo synthesis of deoxyribonucleotides needed for DNA replication and repair. The vast majority of eukaryotes encodes only a class I RNR, but interestingly some eukaryotes, including the social amoeba Dictyostelium discoideum, encode both a class I and a class II RNR. The amino acid sequence of the D. discoideum class I RNR is similar to other eukaryotic RNRs, whereas that of its class II RNR is most similar to the monomeric class II RNRs found in Lactobacillus spp. and a few other bacteria. Here we report the first study of RNRs in a eukaryotic organism that encodes class I and class II RNRs. Both classes of RNR genes were expressed in D. discoideum cells, although the class I transcripts were more abundant and strongly enriched during mid development compared to the class II transcript. The quaternary structure, allosteric regulation, and properties of the diiron-oxo/radical cofactor of D. discoideum class I RNR are similar to the mammalian RNRs. Inhibition of D. discoideum class I RNR by hydroxyurea resulted in a 90% reduction in spore formation and decreased the germination viability of the surviving spores by 75%. Class II RNR could not compensate for class I inhibition during development, and excess of vitamin B12 coenzyme essential for class II activity did not improve spore formation. We suggest that class I is the principal RNR during D. discoideum development and growth, and is important for spore formation, possibly by providing dNTPs for mitochondrial replication. Submitted by Fredrik Soderbom [fredrik.soderbom@icm.uu.se] --------------------------------------------------------------------------- Robustness of self-organizing chemoattractant field arising from precise pulse-induction of its breakdown enzyme: a single cell level analysis of PDE expression in Dictyostelium Noritaka Masakiā, Koichi Fujimotoā, Mai Honda-Kitahara, Emi Hada and Satoshi Sawai ā Both authors contributed equally to this work. Graduate School of Arts and Sciences, The University of Tokyo Biophysical Journal, in press The oscillation of chemoattractant cyclic AMP (cAMP) in Dictyostelium discoideum is a collective phenomenon that occurs when the basal level of extracellular cAMP exceeds a threshold and invokes cooperative mutual excitation of cAMP synthesis and secretion. In order for pulses to be relayed from cell to cell repetitively, secreted cAMP must be cleared and brought down to the sub-threshold level. One of the main determinants of the oscillatory behavior is thus how much extracellular cAMP is degraded by extracellular phosphodiesterase (PDE). To date, the exact nature of its gene regulation remains elusive. Here, we performed live imaging analysis of mRNA transcripts for pdsA - the gene encoding extracellular phosphodiesterase. Our analysis revealed that pdsA is up-regulated during the rising phase of the cAMP oscillations. Furthermore we show by analyzing isolated cells that its expression is strictly dependent on the presence of extracellular cAMP. It is induced only at ~1nM extracellular cAMP, which is almost identical to the threshold concentration for the cAMP relay response. The observed precise regulation of PDE expression together with degradation of extracellular cAMP by PDE form a dual positive and negative feedback circuit, and model analysis shows that this sets the cAMP level near the threshold concentration for the cAMP relay response for a wide range of adenylyl cyclase activity. The overlap of the thresholds could allow oscillations of chemoattractant cAMP to self-organize at various starving conditions making its development robust to fluctuating environment. Submitted by Satoshi Sawai [cssawai@mail.ecc.u-tokyo.ac.jp] ============================================================== [End dictyNews, volume 39, number 4]