Febs Letters Volume 87, Number 1-2./Volume 88, Number 1-2. [antikvár]

Volume 87, number 1 FEBS LETTERS March 1978 Commentary DISCRIMINATION OF MESSENGER RNA Peter HERRLICH Max-Planck-Institut für Molekulare Genetik, Berlin-Dahlem, Germany and Manfred SCHWEIGER Institut für Biochemie der Universität Innsbruck (Naturwiss. Fakultät), 6020 Innsbruck, Austria Received 28 November 1977 1. Introduction Although in the past few years a large number of attempts to transfer and express eukaryotic genes in bacteria have been reported [1-5], confidence seems generally lacking that a eukaryotic messenger can at all be translated efficiently in bacteria. However, only recently has this problem been investigated with sufficient care; There is no efficient heterologous translation of mRNA. We will review here our data on a site specificity in the initiation region of mRNA preventing efficient heterologous translation and discuss briefly the consequences for genetic engineering experiments. We will then summarize recent evidence for mRNA discrimination in general. 2. Results and discussion 2.1. Differences in recognition sites on mRNA of eukaryotic and prokaryotic origin The only possible direct test for the question whether eukaryotic gene copies are translated efficiently in a bacterial cell, is the translation of isolated mRNA in vitro in appropriate systems. A set of messenger RNAs from various organisms was prepared and their translation examined in in vitro protein synthesizing systems from reticulocytes. wheat germ, Krebs ascites cells and E. eoli. The outcome of these experiments was that, except for TMV RNA, all messenger RNAs were translated with drastically different efficiencies (table 1). IVfessenger RNA from eukaryotic cells were translated 200-500-times more efficiently in extracts from eukaryotic cells than in a cell-free system from E. eoli. The reverse was observed for mRNA from prokaryotic sources. These RNAs were translated well in the bacterial extract but by a factor of 50-100 less efficiently in the cell-free systems from nucleated cells. We realize that the protein synthesizing machineries differ in many respects between bacteria and eukaryotic cells [6-9]. The fact, however, that in the same extract two mRNAs can behave so differently, shows clearly that the two messenger RNA species are structurally different. Because the division of the RNAs into two groups followed the cross classification into pro- and eukaryotes, mRNAs from eukary-otes must possess a common structural property which prokaryotic RNA lacks, and vice versa. The tremendous reduction of total protein synthesis, in whatever heterologous combination, suggests that there is a deficiency at the initiation stage. The heterologous recognition sites on mRNA are not rejected completely. The minute quantity of protein made, was still specific and the chains were completed (table 1) [10]. This may explain the long list of publications [11—19] describing successful Elsevier!North-Holland Biomedical Press 1