Question

Genetics Questions

1) A new mutation in Saccharomyces cerevisiae, a eukaryotic yeast, causes the cells to be unable to produce the amino acid histidine. Specifically, they cannot catalyze the first reaction
in the histidine biosynthesis pathway. When examined closely, they are producing a completely wild-type enzyme for this reaction, but at greatly reduced levels. Explain the mutation.

2) If you remove the TATA box and place it immediately upstream of a transcription start site of a eukaryotic gene, and subsequently transcription of the mRNA is assayed, will you still achieve transcription from the same start site?

Answer 1

1) It is a mutation that decreases transcription levels so it can be in the promoter or proximal to promoter elements located upstream of the coding region. These serve as binding sites for RNA Pol II and general transcription factors. Mutations occurring in these regions hinder protein-DNA interactions and thereby reduce transcription.

2)There is no transcription because the TATA box needs to be located at least 25 base pairs upstream of the transcription start site of a eukaryotic gene. The reason is that needs to be space for the assembly of the TATA binding protein and the transcriptions factors involved in the initiation of the transcription with the RNA polymerase at the promoter region.