A student transforms competent E. coli with the pGLO plasmid (encoding GFP under control of the araBAD promoter and an ampicillin resistance gene). After heat shock and recovery, equal volumes of cells are plated on four LB agar plates: (P1) LB only, (P2) LB + ampicillin, (P3) LB + ampicillin + arabinose, (P4) LB + arabinose. Plates are incubated overnight at 37 C.
On which plate(s) will GFP-fluorescent colonies be observed?
- Acheck_circle
P3 only
- B
P1 and P2
- C
P2 only
- D
P1 and P4
Explanation
Ampicillin selects for transformed cells (P2, P3). GFP expression requires arabinose to activate araBAD (P3, P4). Both selection AND arabinose are present only on P3, where transformed colonies fluoresce green.