All internal promoter elements of Neurospora crassa 5 S rRNA and tRNA genes, including the A boxes, are functionally gene-specific.
The internal control elements of Neurospora crassa 5 S genes include an A box and a C box as in Xenopus and Saccharomyces cerevisiae, plus a novel element, the Ribo box at position +18 to +34. The Ribo box is also found in the 40 S rRNA promoter and a ribosomal protein gene but is absent from tRNA genes in N. crassa. The 5 S A box diverges from the tRNA A box consensus at two positions. We tested whether replacement of the 5 S A box with a tRNALeu A box sequence would increase 5 S gene transcription in vitro or would remove the requirement for the Ribo box. The 5 S gene with the tRNALeu A box was transcribed poorly, and the Ribo box and the C box are still required for transcription. We tested the function of the Ribo box and 5 S A box in a tRNA-like transcription unit by constructing hybrids between a 5 S gene and a tRNALeu gene. In the tRNA-like context, the 5 S A box supported a lower level of transcription than the tRNA A box, and the Ribo box was not required at all. Therefore, in N. crassa, all of the 5 S internal control elements are gene-specific. In particular, the 5 S and tRNA A box sequences are not functionally interchangeable and may bind different transcription factors. Transcription of the hybrids was initiated at the 5 S initiation site, suggesting that the mechanism of initiation site selection is the same in the 5 S and tRNA genes. Competition experiments with the tRNA B box suggested that the N. crassa 5 S and tRNA genes require at least one common transcription factor such as TFIIIC.
Shi
Y G
YG
Department of Plant Pathology, University of California, Davis 95616.
Tyler
B M
BM
D001483:Base Sequence; D001667:Binding, Competitive; D003001:Cloning, Molecular; D004271:DNA, Fungal; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012331:RNA, Fungal / Q000235:genetics*; D012341:RNA, Ribosomal, 5S / Q000235:genetics*; D012356:RNA, Transfer, Leu / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism; D019474:Transcription Factors, TFIII; D014158:Transcription, Genetic; D000098832:Transcription Factor TFIIIC
D004271:DNA, Fungal; D012331:RNA, Fungal; D012341:RNA, Ribosomal, 5S; D012356:RNA, Transfer, Leu; D014157:Transcription Factors; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC