Nucleic Acids Research, 1992, Vol. 20, No. 18 4741-4746
© 1992
GENOME STRUCTURE AND MAPPING |
Involvement of the size and sequence of the anticodon loop in tRNA recognition by mammalian and E.coli methionyl-tRNA synthetases
Laboratoire de Biochimie, Unité de Recherche Associée no 240 du Centre National de la Recherche Scientifique, Ecole Polytechnique F-91128 Palaiseau Cedex, France
*To whom correspondence should be addressed
Received July 7, 1992. Revised August 19, 1992. Accepted August 19, 1992.
The rates of the cross-aminoacylation reactions of tRNAsMet catalyzed by methlonyl-tRNA synthetases from various organisms suggest the occurrence of two types of tRNAMet/methionyl-tRNA synthetase systems. In this study, the tRNA determinants recognized by mammalian or E.coli methionyl-tRNA synthetases, which are representative members of the two types, have been examined. Like its prokaryotic counterpart, the mammalian enzyme utilizes the anticodon of tRNA as main recognition element. However, the mamalian cytoplasmic elongator tRNAMet species is not recognized by the bacterial synthetase, and both the initiator and elongator E.coli tRNAMet behave as poor substrates of the mammalian cytoplasmic synthetase. Synthetic genes encoding variants of tRNAsMet, Including the elongator one from mammals, were expressed in E.coli. tRNAsMet recognized by a synthetase of a given type can be converted into a substrate of an enzyme of the other type by introducing one-base substitutions in the anticodon loop or stem. In particular, a reduction of the size of the anticodon loop of cytoplasmic mammalian elongator tRNAMet from 9 to 7 bases, through the creation of an additional Watson-Crick pair at the bottom of the anticodon stem, makes it a substrate of the prokaryotic enzyme and decreases its ability to be methionylated by the mammalian enzyme. Moreover, enlarging the size of the anticodon loop of E.coli tRNAMetm from 7 to 9 bases, by disrupting the base pair at the bottom of the anticodon stem, renders the resulting tRNA a good substrate of the mammalian enzyme, while strongly altering its reaction with the prokaryotic synthetase. Finally, E.coli tRNAMet1 can be rendered a better substrate of the mammalian enzyme by changing its U33 into a C. This modification makes the sequence of the anticodon loop of tRNAMet identical to that of cytoplasmic initiator tRNAMet
Deceased, October 22, 1990
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