Maf1 Protein, Repressor of RNA Polymerase III, Indirectly Affects tRNA Processing

Maf1 is negative regulator of RNA polymerase III in yeast. We observed high levels of both primary transcript and end-matured, intron-containing pre-tRNAs in the maf1 Delta strain. This pre-tRNA accumulation could be overcome by transcription inhibition, arguing against a direct role of Maf1 in tRNA maturation and suggesting saturation of processing machinery by the increased amounts of primary transcripts. Saturation of the tRNA exportin, Los1, is one reason why end-matured introncontaining pre-tRNAs accumulate in maf1 Delta cells. However, it is likely possible that other components of the processing pathway are also limiting when tRNA transcription is increased. According to our model, Maf1-mediated transcription control and nuclear export by Los1 are two major stages of tRNA biosynthesis that are regulated by environmental conditions in a coordinated manner.