Question

Four auxotrophic mutant strains of E. coli (1, 2, 3, 4) are each blocked at a different step of the same metabolic pathway. This pathway involves compounds L, M, N, O, and P. Each of these compounds is tested for its ability to support growth of mutant strains, with the results given below.
(+= growth, ^__ = no growth)

			Compound Used as a Supplement
	L	M	N	O	P
Mutant 1	+	__	+	+	__
Mutant 2	__	__	__	+	__
Mutant 3	+	__	__	+	__
Mutant 4	+	__	+	+	+

Give the order of the compounds in the metabolic pathway and indicate the specific step that is blocked in each mutant strain.

Several sets of double mutations were produced. For example, double mutant 1, 2 has mutant forms for enzymes 1 and 2. Pairs of these double mutations were combined in partial diploids. Would a partial diploid consisting of each of the following pairs of double mutations grow on minimal medium (without supplementation with L, M, N, O, P)?

1,3 and 3,4

1,2 and 3,4

2,4 and 1,2

Answer 1

From the table it is evident that M is the minimal medium

P N L O

Mutant 4 is trp-8 or Trp E + + + +

Mutant 1 is trp -2, -4 or trp D, trp C - + + +

Mutant 3 is trp-3 - - + +

Mutant 2 is trp-1, -6, -7, -9,-10,-11 or trp B - - - +

P - Anthranilate synthetase

N -IGP - indole glycerol phosphate

L - Indole

O - Tryptophan

Order of components - N (IGP) - L (indole) - O (Tryptophan) - P (Anthranilate synthetase)

Mutant 4 - blocks all the four components mentioned above in the synthesis of tryptophan.

Mutant 1 - blocks IGP, indole and tryptophan

Mutant 3 - blocks Indole and tryptophan

Mutant 2 - blocks tryptophan