Question

4. The necessary components for gene expression are often described as either cis-acting elements (“acting from the same molecule”) or trans-acting factors (“acting from a different molecule”). Cis-acting elements are typically sequences that are required for expression. Trans-acting factors are typically proteins that recognize and bind cis-acting sequences to control or facilitate gene expression. For each of the trans-acting factors below, describe their enzymatic activity and one of their cis-acting target sequences. [8 pts; 4 pts each]

4a. RNA Polymerase

4b. Ribosome

Answer 1

4. a. RNA Polymerase:

Enzymatic Reaction:

Nucleoside-triphosphate:RNA nucleotidyltransferase (DNA-directed)

E.coli DNA-dependent RNA polymerase catalyzes the initiation (site selection), elongation and termination of polyribonucleotide chains, using ribonucleoside triphosphates as substrates and DNA as template.

cis-acting target sequence: pribnow box (or TATA box, pribnow is specific to prokaryotes) present -10 nucleotides from start of mRNA.

4. b. Ribosome:

Enzymatic reaction:

ribosomal RNA associates with proteins to form ribosome and catalyzes the formation of peptide bonds between amino acids.

cis-acting target sequence: Internal ribosome entry sequences (IRES)

HCV-like IRESs directly bind the 40S ribosomal subunit to position their initiator codons are located in ribosomal P-site.