Proposed involvement of an internal promoter in regulation and synthesis of mitochondrial and cytoplasmic leucyl-tRNA synthetases of Neurospora.

Abstract

Genetic analysis of an electrophoretic variant of the mitochondrial leucyl-tRNA synthetase [L-leucine:tRNALeu ligase (AMP-forming), EC 6.1.1.4] indicates that it is either an allele of or linked closely to leu-5ts, a mutant that is known to produce a cytoplasmic leucyl-tRNA synthetase with an altered affinity for leucine as well as being deficient in the production of the mitochondrial enzyme. Immunological analysis indicates that the 2 synthetases have little, if any, structural homology. The pattern of synthesis of the enzymes in leu-5ts revertants, the reciprocal relationship of the production of the 2 enzymes in response to a negative regulatory element, presumably of mitochondrial origin, as well as the lack of detectable structural homology, led to the proposal that the phenotype of leu-5ts results from a mutational alteration in the structural gene for the cytoplasmic enzyme in a region involved in the initiation of transcription of the adjacent gene for the mitochondrial enzyme.