Rye nuclease I as a tool for structural studies of tRNAs with large variable arms.

A single-strand-specific nuclease from rye germ (Rn nuclease I) was used for secondary and tertiary structure investigations of tRNAs with large variable arms (class II tRNAs). We have studied the structure in solution of two recently sequenced tRNA(Leu): yeast tRNA(Leu)(ncm5UmAA) and bovine tRNA(Leu)(XmAA) as well as yeast tRNA(Leu)(UAG), tRNA(Leu)(m5CAA) and tRNA(Ser)(IGA). The latter is the only tRNA with a long variable arm for which the secondary and tertiary structure has already been studied by use of chemical probes and computer modelling. The data obtained in this work showed that the general model of class II tRNAs proposed by others for tRNA(Ser) can be extended to tRNAs(Leu) as well. However interesting differences in the structure of tRNAs(Leu) versus tRNA(Ser)(IGA) were also noticed. The main difference was observed in the accessibility of the variable loops to nucleolytic attack of Rn nuclease I: variable loops of all studied tRNA(Leu) species were cut by Rn nuclease I, while that of yeast tRNA(Ser)(IGA) was not. This could be due to differences in stability of the variable arms and the lengths of their loops which are 3 and 4 nucleotides in tRNA(Ser)(IGA) and tRNAs(Leu) respectively.