Hybridization of mitochondrial transfer RNA and mitochondrial DNA in petite mutants of yeast

Abstract

The hybridization of mitochondrial leucyl- and mit-valyl-tRNA's with mitochondrial DNA of a series of petites has been used to characterize some of the changes in petite mit-DNA. The spontaneously mutated petite strain used (R1-6) was found to be heterogeneous with respect to hybridization with mitt-RNA's. Mit-DNA's isolated from subclones of the original strain differed in their ability to hybridize with grande mit-valyl- and mit-leucyl-tRNA's. Hybridization of mit-DNA of all petite subclones with grande mit-leucyl-tRNA resulted in apparent saturation levels that were equal, or usually two- to sixfold greater, than obtained with grande mit-DNA. In contrast, the ability to hybridize with grande mit-valyl-tRNA was lost by mit-DNA of some subclones, and partially retained in others. Mitochondrial leucyl- and valyl-tRNA's isolated from some petite strains retained their capacity to be aminoacylated in vitro, and were able to hybridize with mit-DNA of grande and some petite strains. The pattern of hybridization of petite mit-tRNA with mit-DNA from petite subclones was similar to that obtained with grande mit-RNA. Unlabeled mit-tRNA, but not supernatant tRNA, competed with the hybridization of both grande and petite tRNA's with grande and petite mit-DNA. Melting of the grande mit-tRNA petite mit-DNA hybrid resulted in a sharp curve with a T m equivalent to about 71 °C in 2 × standard saline citrate.