Identification and cellular localization of the exosome subunits in testis of Lithobates catesbeianus (Bullfrog)

Abstract

The exosome is a 3'-5' exoribonucleolytic complex present in many organisms, from archaea to higher eukaryotes. It is involved in processing and degradation of different kinds of RNAs. In archaea, the exosome is composed of three different subunits, two containing RNase PH domains, and one containing RNA binding domains KH and S1. Structural data on the archaeal exosome show that the two subunits with RNase PH domains, aRrp41 and aRrp42, form heterodimers and three dimers form the RNase PH ring, responsible for catalysis, to which three molecules of either aRrp4 or aCsl4 (RNA binding proteins) bind on one side. Sequence analysis of the exosome subunits, protein-protein interaction data, electron microscopy data of the complex and crystallography analysis indicate that the exosome complexes from different organisms have a common basic structure. In eukaryotes, however, the exosome is composed of eleven different subunits, nine of them forming a complex similar to the archaeal exosome, but without catalytic activity. Two additional subunits, which are catalytically active, bind to different sides of the complex. Although the exososme has been shown to be conserved throughout evolution, this complex has yet to be described in many organisms. Recently, protein imunolocalization data indicate that the exosome subunits may assume different localization in eukaryotic cells during the cellular division. In addition, the Rrp44p exosome subunit has been shown to be essential for the correct chromosome segregation, whereas Rrp6p is involved in meiotic division. These data suggest that the exosome activity is important for the control of cell division. The main goal of this project is the characterization of the exosome in meiotic cells, using the testicular tissue of bullfrog as a system. The exosome has not yet been described in this organism, and in this system we can assess the localization and expression levels of the exosome subunits in the testicular tissue, which will enable this assessment in somatic and germ cells. (AU)