Practice Questions

TLS Online TPP Program

#Question id: 15652

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. You have isolated a mutation that causes constitutive melibiase activity, which you designate MelA–. P1 phage mapping experiments using a Tn5 insertion linked to Mel1 show that MelA– is not linked to Mel1. Moreover you find that when an amber suppressor is introduced into a MelA– mutant, normal melibiase regulation is restored. Classify the MelA– mutation in terms of its basic genetic properties,

#SCPH01 Biochemistry

MelA- as a recessive, loss of function mutation, whose wild-type allele codes for a cis-acting factor.
MelA- as a recessive, loss of function mutation, whose wild-type allele codes for a trans-acting factor.
MelA- as a dominant, gain of function mutation, whose wild-type allele codes for a trans-acting factor.
MelA- as a dominant, gain of function mutation, whose wild-type allele codes for a cis-acting factor.