4. One of the genes of the E. coli Lysine operon (LysA) encodes an enzyme necess

Question

4. One of the genes of the E. coli Lysine operon (LysA) encodes an enzyme necessary to synthesize lysine. The operon encodes several other 'genes' LysB. LysC and Lysh. Following is a table of data from different lysine backgrounds, including partial diploids 'A' represents LysA gene and D' represents LysD. gene. Superscript + indicates a normal copy of the gene. All other supsersciipts indicate abnormal. A plus indicates that the enzyme LysA is produced (ie transcribed and translated) and is active, whereas a minus indicates it is not produced. a. On the basis of these results, does the LysD gene encode a regulator protein or an operator? 1pt) b. Do these data suggest that the ys operon is negatively or positively controlled? ls it repressible or inducible? explain your answer. (2pts) c. What type of mutation is D5? (1pt) Genotype D A- DA Lysine absent Lysine present

Explanation / Answer

The given operon is a synthetic operon i.e, gene present in the operon mediate lysine biosynthesis.

When Lys is present, the operon is repressed.

When Lys is absent, the operon is activated.

So, it is negative repressible operon.

When D is absent (D-), the operon is insensitive to the presence or absence of Lys.

D- mutation could be complemented in trans. So, D must be a diffusible product (i.e, repressor protein).

Ds mutation renders the repressor protein constitutively bind to the operator irrespective of the presence or absence of Lys.

It is a constitutive mutation.

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