The requirement for the A block promoter element in tRNA gene transcriptionin vitrodepends on the ionic environment

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Abstract
When yeast cell extracts that faithfully transcribe class III genes are provided with different electrolyte ions, the pattern of transcripts changes. A transcription unit in pBR322, silent with 0.1K potassium chloride, becomes active in the presence of 0.1M potassium acetate. This pseudogene depends on transcription factors B and C and RNA polymerase III like a tRNA gene. The transcribed region contains the only sequence in pBR322 homologous to the modified B block consensus sequence GTTCRDNNC found in normal tRNA genes. The presence of a block A sequence is less evident. When a block A deleted tRNA gene was constructed, it behaved similarly: poorly transcribed with 0.1M potassium chloride, well transcribed with 0.1M potassium acetate. In fact, the deletion of the A block promoter element from the tRNA gene did not dramatically lower its transcription when tested with potassium acetate, while it had a strong negative effect when tested with potassium chloride. Consequently the requirement for this promoter elemant is not constant but is a function of the electrolyte composition.