Question

For each of the following, indicate if it is cis-acting or trans-acting

A regulatory gene that codes for a transcription factor _______________

A promoter _______________

An operator _________________

An enhancer _________________

Answer 1

Cis-acting regulatory elements are the DNA sequences, generally in the vicinity of the gene, that act to modulate expression of genes on the same molecule by binding with regulatory proteins. Trans-acting elements are DNA sequences that code for proteins, or factors which bind to DNA sequences, generally the cis-acting elements, to regulate gene expression. These proteins may bind to any DNA strand in the cell, not specifically the same molecule which contains the encoding sequence.

1. A regulatory gene that codes for a transcription factor is trans-acting; the transcription factor encoded by this gene, binds to DNA sequences such as promoter, to regulate target gene transcription.

2. A promoter is cis-acting; it binds with proteins such as transcription factors, and RNA polymerase, to initiate downstream gene transcription.

3. A operator is cis-acting; the binding of repressor protein at the operator results in inhibition of the transcription of target gene.

4. An enhancer is cis-acting; it is a short sequence, which may be located near or far from the gene. Binding of activator or transcription factors at the enhancer region can lead to increased transcription of the target gene.