MCB421 HOMEWORK #1 FALL 2008
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1. NADP is an essential cofactor for many cellular processes. Because it is not
transported, exogenous NADP cannot supplement mutants unable to synthesize
intracellular NADP. Five independent mutations were obtained that affect the
synthesis of NADP. The properties of the mutations are described in the table
below (where + indicates growth on rich medium, - indicates that no growth on
rich medium, and -/+ indicates weak growth on rich medium).
Row Mutation Growth temperature
#30°C 42°C 30 42°C 42 30°C
1nad+ + + +
2nad-601 + -
3nad-602 + -
4nad-603 + -
5nad-604 - +
6nad-606 -/+ -/+
7nad-607 - +
8nad-601 nad-602 + - + +
9nad-601 nad-603 + - + +
10 nad-601 nad-604 - - - +
11 nad-601 nad-607 - - + -
12 nad-604 nad-607 - + + +
a. Note the properties of nad-601, nad-602, nad-603, nad-604, nad-606, and
nad-607 in the above Table. Indicate both whether the mutant has a conditional
phenotype (temperature sensitive, cold sensitive, or non-conditional) and
whether the allele is likely to be due to a missense, nonsense, frameshift,
deletion, or insertion mutation? Briefly explain your answers.
b. Interpret the results for each pair of double mutants in rows # 8-12. If you are
not able to determine the order of the reactions catalyzed by some of the gene
products from the data given, suggest a likely reason for this result.
2. You have LB (rich medium) cultures of two E. coli strains. One is a
temperature sensitive (TS) leucine auxotroph and the second contains a TS
mutation in the rpoA gene that codes for the alpha subunit of RNA polymerase.
a.) Which mutation is most likely to affect an essential function? Why?
b.) Using a simple agar plate test, how could you distinguish the two strains?
Be sure to include the composition of the media you would use and the
temperature(s) you would incubate the plates.
c.) Which class (i.e. point mutant, deletion, insertion, etc.) are these mutants
likely to be? Why?
