ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS 166, 17-25 (1973) The Characterization of the tRNAs and Aminoacyl-tRNA Synthetases of the Blue-Green Alga, Anacystis nidolans’ NICOLE BEAUCHEMIN, BERNARD LARUE AND R. J. CEDERGREN Dbpartenrent de Biochimie, Uuioersit& de Montrbal, Case Postale 6128, Monkhal 101, (L)&hec Received October 16, 1972 The tRNA and aminoacyl-tRNA syntheta,ses of the blue-green alga, Anacystis nidulans have been isolated and studied. The dist,ribution of some algal tRNA species on BD-cellulose chromatography has been determined. One tRNAMetspecies has been isolated in SOY0 purity by a single chromatography on a BD-cellulose column de- veloped with a modified salt gradient. The number of different tRNA isoacceptors for Met, Ser, and Leu has been ascertained by RPC-5 chromatography. The recognition of algal tRNAs by the homologous algal synthetase preparation as well as the heter- ologous Escherichia coli preparation was studied by the aminoacylation tests. Since all of the isoaccepting species of the tRNAs tested behaved almost identically in pres- ence of the two enzyme preparat,ions, a conservation of the recognition site during the evolutionary divergence of bacteria and algae is strongly suggested. The comparison of the primary structures of macromolecules has proven t’o be an effective means of determining the phy- logeny of organisms (1). Recently, transfer RNAs have been cited as a source of new data for the study of molecular evolution (2-5). Comparison of the some forty se- quences presently determined (for a review, see Ref. 2) shows tRNA sequences to be extremely conservative during the evolu- tionary process (R. Morazain and R. J. Cedergren, unpublished work). One may postulate, therefore, that tRKA primary structure will be particularly useful in t,he elucidation of the relationship between more distant organisms, such as the various pro- karyotes. Many bacterial tR?;A sequences are cur- rently available, especially numerous are those of Escherichia coli (2), although tRNA sequences have been determined as well from Staphylococcus epidermis (6) and Sal- monella typhimurium (7). Of particular in- t,erest was the observation that the tRiYAHia of E. coli and S. typhimurium have identjical 1 This study was supported by the Medical Re- search Council of Canada. sequences, thus corroborating the earlier postulate of the conservative evolution of tRNAs. In addition, the tRNAs of several mycoplasmas have been isolated (8), and tRNA1le from Mycoplasma sp. (kid) has been well characterized in preparation for sequence studies (9). An important family of prokaryotes is the blue-green algae. To date no information has appeared on the tRNAs of this group of organisms. The possibility of comparing algal tRNA sequences and functions with those of other organisms has led us to study the blue- green alga, Anacystis nidulans. The isola- tion and characterization of the tRKAs and aminoacyl-tRNA synthetases of A. nidulans are reported. Special attention was given t,o the leucine and serine-accepting species, since the sequence of these tRNAs may be of particular interest in the evolution of tRNAs (3). MATERIALS AND METHODS Organism Anacystis nidulaus strain 626, described by Kratz and Myers (IO), was obtained from the Algal Culture Collection of the University of Indiana. 17 Copyright 0 1973 by Academic Press, Inc. All rights of reproduction in any form reserved.