Use this information to answer the next three questions. (GRE) Researchers study

Question

Use this information to answer the next three questions. (GRE) Researchers studying the activity of a gene controlled by a steroid hormone isolated 750 bp of DNA immediately preceding the start site of transcription (+1). They demonstrated that if these sequences are cloned upstream of the reporter gene, bacterial chloramphenicol acetyltransferase (CAT), and the recombinant DNA is then introduced into mammalian cells, CAT enzyme activity increases in response to hormone treatment. In order to identify promoter sequences involved in regulation of this gene, they made a series of deletions containing various regions of the 5 regulatory sequences and cloned these upstream of the CAT reporter gene as shown in the figure below. The clones were then introduced into mammalian cells and CAT enzyme activity was assayed in the absence (-) and presence (+) of hormone. The figure shows results of a representative 5 regulatory sequences Hormone:- -742 CAT gene CAT gene CAT gene CAT gene CAT gene CAT gene CAT gene 0.02 21 212 -638 228 54 59 27 -424 -315 -116 tE ] 5. 0.02 0.02 OAssuming that there is a single hormone responsive element in the promoter, that element is located between a. -742 and -638 b. -638 and-424 c. 424 and-315 d. -315 and-116 e. -116 and -27 hich statement is NOT supported by the data? a. The bacterial CAT gene requires eukaryotic gene regulatory sequences for significant expression in mammalian cells b. The presence of hormone increases transcription of the hormone responsive reporter gene 10-fold c. There are hormone-Independent regulatory sequences downstream of -315 in the promoter d. There are hormone-independent regulatory sequences upstroim of -315 in the promoter e. Regulatory sequences do not lie upstream of -742 in the hormone responsive promoter

Explanation / Answer

1. Option B is correct.

When the region between -638 bp to -424 bp is deleted, the CAT activity reduced darstically. This indicates that the deleted region contains a hormone responsive element.

2. Option D is correct.

Hormone responsive element is presumably located the region between -638 bp to -424 bp which is upstream to -315 bp

3. DNA methylation and histone modifications are the major epigenetic changes that have been described in detail. DNA methylation that occurs at the fifth carbon atom of the cytosine in the CpG islands is characteristic to each tissue and also shows specificity with respect to developmental stage and age.

DNA methylation is an epigenetic reversible modification that occurs at the 5th carbon atom of the cytosine residues in CG-dinucleotide sequence (CpG Island). It is dynamic in nature and varies depending on the age, tissue type, environmental factors, pathogens and nutritional status.

DNA methylation is repression mark. So, if the regulatory elements are methylated, rDNA would not be expressed.

Related Questions

Navigate

• Browse (All)
• Browse U
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.