John Rawls

jrawls's picture
  • Professor Emeritus
  • Biology
Education

Ph.D. Univ. of North Carolina, 1973

Research

My primary research interests are understanding the relationships of gene structure and expression during development. Using the model organism Drosophila melanogaster with which to study the genes and proteins controlling pyrimidine levels in cells, two separate and very interesting projects have emerged in recent years and are current objectives of research in my lab.

     Pyrimidine degradation and neurogenesis animals. In animals, a family of structurally similar proteins have evolved from a single protein found in prokaryotes and simpler eukaryotes. The animal dihydropyrimidinase (DHP) protein carries out the ancestral enzymatic role in pydrimidine degradation, whereas the collapsin response mediator protein(s) (CRMP) mediates neuronal growth cone collapse during central nervous system development. How these protein variants evolved and the exact role of CRMP in the establishment of neuronal circuitry are poorly understood. Vertebrates have a multi-gene family that generates the distinctive members of the DHP/CRMP protein family; the variety of members of that family (at least five in mammals) complicates their biological understanding. Insects, however, have a single gene that gives rise to two protein forms (DHP and a single CRMP) by differential mRNA splicing. Thus Drosophila offers a simple and powerful experimental system with which to understand the divergent biological roles of these proteins. Using genetic and developmental methods, we have created mutations of both fly proteins as well as a variety of transgenic tools. Several experimental tracks are underway to dissect the functions of these proteins: developmental analysis of knockout mutants; using GFP fusion constructs to determine the expression patterns of these proteins in tissues and cells; behavioral studies of mutant animals to identify specific neurogenic defects.

     Translational control during spermatogenesis. Regulation of protein synthesis is a prominent feature of gametogenesis in animals. Spermatogenesis is especially subject to translational regulation, because most mRNAs that direct the extensive remodeling of the cell to form a spermatozoon (i.e., spermiogenesis) must be transcribed days earlier in pre-meiotic spermatocytes. mRNA for one of the genes controlling de novo pyrimidine biosynthesis (dhod) is synthesized in an abundant and unusual form during Drosophila spermatogenesis. We have shown that this transcript arises from use of a spermatocyte-specific promoter, and that this RNA is subject to a translational-delay system that operates during spermatogenesis, such that the protein product is made several days after synthesis of the RNA. A 36-nucleotide sequence within the 5´ end of this RNA directs its sequestration and translational delay, and we have identified a testis protein that binds to this sequence. These findings offer an opportunity to analyze components of the cellular machinery that performs RNA sorting, sequestration and timely translation. We have identified several novel genes required for dhod RNA sequestration during spermatogenesis, the most interesting of which is a research focus in the lab. This gene, ped, is required for delayed translation of mRNA bearing the dhod sequestration signal; ped mutants precociously translate these mRNAs. In early spermatogenesis, PED protein initially appears in the nucleus, then moves to the cytoplasm, apparently as part of a ribonucleoprotein complex. Orthologs of this protein are found in a variety of other animals, including humans. We are pursuing both biochemical and genetic studies to better understand PED and its partners in this translational delay pathway in animals.

Graduate Training
Selected Publications: 
  • Yang, J., L. Porter J. Rawls (1995). Expression of the dihydroorotate dehydrogenase gene, dhod, during spermatogenesis in Drosophila melanogaster. Molecular and General Genetics 246:334-341.
  • Porter, L., J. Yang J. Rawls (1995) Expression of the de novo pyrimidine biosynthesis genes during spermatogenesis in Drosophila melanogaster. Purine Pyrimidine Metabolism in Man VIII (A. Sahota and M. Taylor, eds.), Plenum Press, NY. pp. 567-573.
  • Simmons, A., J. Rawls, J. Piškur J. Davidson (1999). A mutation that uncouples allosteric regulation of carbamyl phosphate synthetase in Drosophila. Journal of Molecular Biology 287:277-285.
  • Rawls, J., W. Knecht, K. Diekert, R. Lill M. Löffler (2000). Requirements for the mitochondrial import and localization of dihydroorotate dehydrogenase. European Journal of Biochemistry 267:2079-2087.
  • Löffler, M., W. Knecht, J. Rawls, A.. Ullrich C. Dietz (2002) Drosophila melanogaster dihydroorotate dehydrogenase: the N-terminus is important for biological function in vivo but not for catalytic properties in vitro. Insect Biochemistry and Molecular Biology 32:1159-1169.
  • Rawls, J. (2006) Analysis of pyrimidine catabolism in Drosophila melanogaster using epistatic interactions with mutations of pyrimidine biosynthesis and ß-alanine metabolism.  Genetics 172:1665-1674.
  • Syrzycka, M., L. McEachern, J. Kinneard, K. Prabhu, K. Fitzpatrick, S. Schulze, J. Rawls, V. Lloyd, D.  Sinclair B. Honda (2007) The pink gene encodes the Drosophila orthologue of the human  Hermansky-Pudlak syndrome 5 (HPS 5) gene. Genome 50:548–556.

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