Relation entre la structure et le coefficient de partage des tRNA de levure dans les systèmes solvants salins

Abstract

Relation between the structure and the partition coefficient of yeast tRNA's in saline solvent systems The relationship between the structure of thirteen yeast tRNA's of known sequence and their partition coefficients K was studied. tRNA's were fractionated by counter-current distribution in “saline solvent systems” composed of an inorganic component of high molarity (phosphate or sulphate) and various organic components (acid, amide, or ether—alcohol). The behaviour of the tRNA's does not depend on the nature of the saline solvent used. It conforms to the following basic equation: log K = c(A/A + G)(Pu/Py) + d or c(A/Py) + d tRNA Asp and tRNA Val are notable exceptions to this law. Their partition coefficients can be explained by the low amounts or the complete loss of alkylated bases in the anticodon region. The marked decrease in K when tRNA's lose their 3′-terminal adenosine and some considerations from a statistical analysis of the base distribution and the number of homologous sequences (and their intramolecular position) suggest that there are at least two confomational factors commom to yeast tRNA's solubilized in a medium of high ionic strength: an exposed anti-codon region on the one hand and the 3′-terminal adenosine, which is apparently involved in a structure more expanded than that of the tRNA without 3′-terminal adenosine, on the other hand.