Question

1.Where areDNase I hypersensitivity sites found, and what do they indicate about the nature of chromatin?

2.What is a response element? How do response elements bring about the coordinated expression of eukaryotic genes?

3.Briefly list some of the ways in which siRNAs and miRNAs regulate genes.

Answer 1

1. DNAse I hypersensitivity assay is used to detecting the protein binding sites on DNA molecules.
The protein-bound sites are protected from DNAse I digestion. These sites indicate heterochromatin (Tightly compacted DNA with the help of histones)
Heterochromatin = Transcriptionally inactive
The unbound sites are subjected to DNAse I digestion. These sites indicate heterochromatin (Loosely compacted DNA)
Euchromatin = Transcriptionally active

2. A response element is a cis-acting sequence element found in the DNA or RNA sequence.
They regulate the expression of the associated sequences.
They can be directional. Ex: Promoter and operator
They can be non-directional. Ex: Enhancer and silencer
A transcription factor that recognizes a shared response element in the promoters of similar genes can regulate their coordinated expression.

3. siRNAs and miRNAs exert post-transcriptional gene regulation.
a. They can mediate target transcript cleavage
b. They can mediate translational inhibition of the target transcript