Yeast Class III gene transcription factors and RNA polymerase III were used to form ternary transcription complexes on a tRNASer gene in vitro under UTP-limiting transcription conditions. These ternary transcription complexes were composed of template DNA, proteins, and RNA. We have shown that the RNAs contained in these complexes represented specifically initiated nascent pre-tRNASer transcripts. These nascent RNAs could be very efficiently elongated to full-length pre-tRNASer molecules, even in the presence of the ionic detergent sarcosyl. Partial purification (greater than 100-fold) of these sarcosyl-resistant ternary transcription complexes could be achieved in a single step via sucrose gradient sedimentation. Comparable sarcosyl-resistant ternary transcription complexes could not be formed using purified yeast RNA polymerase III as the only protein component of the complex.