The complexity of mitochondrial tRNA import.

Import of nucleus-encoded, cytoplasmic tRNAs into mitochondria to compensate evolutionary loss of the corresponding mitochondrial genes has been documented in a large number of species. Although the phenomenon has been known for more than 25 years, it was only recently that the mechanism of tRNA import started receiving the sustained attention of workers investigating yeast, protozoal and higher plant systems. The purpose of this review is to summarize recent developments that shed new light on the selectivity of the process, the identity of the import apparatus and the nature of the bioenergetic transactions leading to tRNA translocation, and to build a working model of the import complex suggested by these observations.