Chapter 13, Problem 18P

Summary Introduction

To analyze:

The expression of UG $4$ gene occurs in leaf and stem tissue of plant Arabidopsis thaliana. To study the process of regulation of UG $4$ gene expression, six small deletions are introduced at the DNA sequence upstream of the gene coding sequence. The site of deletions and their impacts on UG $4$ gene expression are shown in the figure of question.

From the given information, following questions are asked.

Explanation on reason for different impacts of deletions B and F on expression in stem tissue and leaf tissue.

Explanation on reason for deletion of D allows UG $4$ gene expression in leaf tissue but not in stem tissue.

Explanation on reason for deletion of E reduces UG $4$ gene expression in leaf tissue but not in stem tissue.

Introduction:

A eukaryotic gene has regulatory sequences which comprises of promoters, enhancers, and silencers which collectively control the gene expression.

Enhancers are present upstream of the promoter sequence. Binding of the enzymes and the transcription factor to the enhancer sequences bring about the regulation of the transcription of the gene. Enhancers are termed as positive cis acting elements as they act on the gene present on the same strand; it can also affect the gene which is $\text{1000}$ bp away. Enhancers aid in increasing the basal level transcription of the gene expression while the silencers are the negative regulatory sequences which bind to the repressor sequences keeping the gene in the repressed state.

Promoter is the sequence of nucleotides on DNA where RNA polymerase is recruited to carry out the transcription of the particular gene. Promoters’ sequences are observed to highly conserve through evolution therefore calling them consensus sequences. In prokaryotes, the promoter comprises of the sequence called as TATA BOX (TATAAT) at $\text{-10}$ and PRIBNOW BOX at $\text{-35}$(TTGACA). Promoter and Enhancer present in the upstream together bring out the maximum expression of the gene.