You want to test a hydroxylating agent that adds an -oh group for mutagenicity by

You want to test a hydroxylating agent that adds an -oh group for mutagenicity by doing the ames test. hydroxylamine adds -oh to cytosine, and hydroxylated c pairs with a instead of g. there are different types of his- auxotrophs that you can choose from in order to detect reversion to his+ prototrophs in response to a compound under test. what type of his- mutants do you need to use for testing hydroxylamine in the ames test?