dictyNews Electronic Edition Volume 38, number 17 July 6, 2012 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 Retinoblastoma Orthologue is a Major Regulator of S-phase, Mitotic, and Developmental Gene Expression in Dictyostelium' Kimchi Strasser1, Gareth Bloomfield2, Asa MacWilliams3, Adriano Ceccarelli4, Harry MacWilliams5, Adrian Tsang1 1 Biology Department and Centre for Structural and Functional Genomics, Concordia University, Montreal, QC, Canada 2 MRC Laboratory of Molecular Biology, Cambridge, UK and Wellcome Trust Sanger Institute, Hinxton, UK 3 Siemens Corporate Technology, Munich, Germany 4 Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Italy 5 Biozentrum der Ludwig-Maximilans-UniversitŠt, Munich, Germany PLoS ONE, in press The retinoblastoma tumour suppressor, Rb, has two major functions. First, it represses genes whose products are required for S-phase entry and progression thus stabilizing cells in G1. Second, Rb interacts with factors that induce cell-cycle exit and terminal differentiation. Dictyostelium lacks a G1 phase in its cell cycle but it has a retinoblastoma orthologue, rblA. Using microarray analysis and mRNA-Seq transcriptional profiling, we show that RblA strongly represses genes whose products are involved in S phase and mitosis. Both S-phase and mitotic genes are upregulated at a single point in late G2 and again in mid-development, near the time when cell cycling is reactivated. RblA also activates a set of genes unique to slime moulds that function in terminal differentiation. Like its mammalian counterpart Dictyostelium RblA plays a dual role, regulating cell-cycle progression and transcriptional events leading to terminal differentiation. In the absence of a G1 phase, however, RblA functions in late G2 controlling the expression of both S-phase and mitotic genes. Submitted by Kimchi Strasser [kimchi@gene.concordia.ca] -------------------------------------------------------------------------------------- Conservation and divergence between cytoplasmic and muscle-specific actin capping proteins: insights from the crystal structure of cytoplasmic Cap32/34 from Dictyostelium discoideum. Eckert C, Goretzki A, Faberova M, Kollmar M. BMC Struct Biol. 2012 Jun 1;12(1):12. [Epub ahead of print] http://www.biomedcentral.com/1472-6807/12/12/abstract BACKGROUND: Capping protein (CP), also known as CapZ in muscle cells and Cap32/34 in Dictyostelium discoideum, plays a major role in regulating actin filament dynamics. CP is a ubiquitously expressed heterodimer comprising an alpha- and beta-subunit. It tightly binds to the fast growing end of actin filaments, thereby functioning as a "cap" by blocking the addition and loss of actin subunits. Vertebrates contain two somatic variants of CP, one being primarily found at the cell periphery of non-muscle tissues while the other is mainly localized at the Z-discs of skeletal muscles. RESULTS: To elucidate structural and functional differences between cytoplasmic and sarcomercic CP variants, we have solved the atomic structure of Cap32/34 (32 = beta- and 34 = alpha-subunit) from the cellular slime mold Dictyostelium at 2.2 A resolution and compared it to that of chicken muscle CapZ. The two homologs display a similar overall arrangement including the attached alpha-subunit C-terminus (alpha-tentacle) and the flexible beta-tentacle. Nevertheless, the structures exhibit marked differences suggesting considerable structural flexibility within the alpha-subunit. In the alpha-subunit we observed a bending motion of the beta-sheet region located opposite to the position of the C-terminal beta-tentacle towards the antiparallel helices that interconnect the heterodimer. Recently, a two domain twisting attributed mainly to the beta-subunit has been reported. At the hinge of these two domains Cap32/34 contains an elongated and highly flexible loop, which has been reported to be important for the interaction of cytoplasmic CP with actin and might contribute to the more dynamic actin-binding of cytoplasmic compared to sarcomeric CP (CapZ). CONCLUSIONS: The structure of Cap32/34 from Dictyostelium discoideum allowed a detailed analysis and comparison between the cytoplasmic and sarcomeric variants of CP. Significant structural flexibility could particularly be found within the alpha-subunit, a loop region in the beta-subunit, and the surface of the alpha-globule where the amino acid differences between the cytoplasmic and sarcomeric mammalian CP are located. Hence, the crystal structure of Cap32/34 raises the possibility of different binding behaviours of the CP variants toward the barbed end of actin filaments, a feature, which might have arisen from adaptation to different environments. Submitted by Martin Kollmar [mako@nmr.mpibpc.mpg.de] ============================================================== [End dictyNews, volume 38, number 17]