Transcription of a yeast ribosomal RNA minigene in Saccharomyces cerevisiae.

A transcription system using intact yeast has been developed for investigating which sequences are implicated in the initiation of transcription of yeast rRNA genes. The system employs an rRNA minigene that consists of the initiation and termination sites for rRNA biosynthesis separated by approx. 700 base pairs of vector DNA in the Escherichia coli-yeast shuttle vector, pJDB207. Two recombinants containing this minigene were constructed; one retained all of the nontranscribed spacer DNA upstream from the initiation site, the other retained 208 base pairs of this DNA. Transcripts of this structurally unique minigene in RNA from yeast transformed with these recombinants were readily detected by nuclease S1 mapping. These transcripts were initiated at the site used by the host rRNA genes, were approx. 3-fold more abundant in the recombinant retaining all of the nontranscribed spacer and were less abundant when the yeast was not growing.