You are studying a new strain of E. coli that can utilize the disaccharide melibiose very efficiently. You find that utilization depends on the enzyme melibiase, which is encoded by the gene Mel1. Mel1 is not expressed unless melibiose is present in the growth medium.

Next, you isolate a third mutant, MelC–, which gives constitutive melibiase expression. The MelC– mutation is closely linked to Mel1 and MelB–. Genetic tests of the MelC– mutation yield the following:

 

As above, classify the MelC– mutation in terms of its basic genetic properties and explain how you arrived at your conclusions.

#Question id: 4266

#Unit 3. Fundamental Processes

48S pre initiation complex is

#Question id: 4267

#Unit 3. Fundamental Processes

The 3D structure of the complete Escherichia coli ribosome with bound mRNA and tRNAs revealed that the very amino terminus of one protein (L27) does reach into the active site. This finding suggested a role for this protein in catalysis. To test this possibility, the nine amino acids at the L27 amino terminus that were in close proximity to the active site were eliminated by mutation. The following possible outcomes were found to be correct as

A. The resulting cells produced ribosomes with reduced but detectable peptidyl transferase activity

B. Region of the L27 protein contributes to peptidyl transferase activity

C. The mutant ribosomes, didn’t synthesised wildtype levels of cells

D. Vast majority of this increase in peptide bond formation is retained, even without the presence of L27 in the active site

E. The most likely role for L27 is to correctly position one or more of the RNA components of the active site

#Question id: 4268

#Unit 3. Fundamental Processes

23S rRNA catalyze peptide-bond formation as

A. base pairing between the 23S rRNA and the CCA ends of the tRNAs

B. A- and P-sites positions the a-amino group of the aminoacyl-tRNA to attack the carbonyl group of the growing polypeptide attached to the peptidyl-tRNA

C. Entropic catalysis is involved

#Question id: 4269

#Unit 3. Fundamental Processes

The kinase P-TEFb

A. Is recruited to polymerase by transcriptional activators

B. Phosphorylates the serine 2&5 of the CTD repeats for elongation

C. Phosphorylates SPT5 and TAT-SF1

#Question id: 4270

#Unit 3. Fundamental Processes

RNA helicase contains characteristic

#Question id: 4271

#Unit 3. Fundamental Processes

To participate successfully in the peptidyl transferase reaction, the tRNA must rotate into the peptidyl transferase center of the large subunit in a process called as