MG2-PROPERTIES OF TRNA(PHE) AND ITS GENE TRANSCRIPT( IONS DIFFERENTLYAFFECT THE PHYSICAL)

The tRNAs isolated from cells always contain modified nucleosides (min ers) occupying specific positions in the primary structure. The transc ripts of tRNA genes enzymatically synthesized in vitro are free from m iners. Therefore, the comparison of mature tRNAs and the transcripts p rovides an opportunity to reveal the role of modifications in creating the spatial structure of tRNA. In this work, we compared the mature t RNA(Phe) from Escherichia coli and the gene transcript of the same tRN A. The analysis of differential melting curves showed that, at low Mg2 + concentrations (<1 mM), the transcript lacked certain elements of sp atial structure. Circular dichroism and absorption spectra indicated d ifferent sensitivity of the secondary structure of the two forms of tR NA to divalent cations, while the character of structural transitions remained similar. Measurement of the hydrodynamic dimensions of mature tRNA and the transcript indicate a weak influence of modifications on the general shape of the molecule. The post-transcriptional modificat ions were shown to exert a substantial effect on the local conformatio n of the molecule in the presence of divalent cations, leaving the who le three-dimensional structure of the tRNA molecule unaltered.