A colleague sends you six newly isolated E. coli ade auxotrophic mutants (ade 1

Question

A colleague sends you six newly isolated E. coli ade auxotrophic mutants (ade 1 through ade 6). You infect each with your theta theta ade+ phage and isolate phage in which each ade mutation has been crossed onto the phage chromo (= theta theta ade1 through 6). These six ade phage are now used to lysogenize the six ade bacteria in every pair-wise combination. As depicted in the table below, some combinations allowed growth without adenine added to the media ("+"), while other failed to grow on adenine-free media From this data, how many ade genes have been identified by this set of six mutants? Also, describe which mutations affect which genes (you may name the genes any way you like; e.g. adeA, adeB, etc.).

Explanation / Answer

The number of ade genes identified from this set can be calculated by working out the the number of complementation groups present.

Three points to identify complementation groups are :

(i) A mutant never complements itself.

(ii) Growth occurs (+) means that the mutants complement each other. When mutants complement it means that they belong to different complementation group.

(iii) Growth did not occur (-) means that the mutants do not complement each other. When mutants do not complement it means that they belong to the same complementation group.

There are 3 complementation groups that are identified:

(i) 1

(ii) 2,4 and 5

(iii) 3 and 6

This means that there are at least 3 genes that can be identified from this set.

Mutation 1 affects adeA gene, mutation 2,4 and 5 affects adeB gene, mutation 3 and 6 affects adeC gene.

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