Two thymidylate synthetases in Bacillus subtilis.

Abstract
B. subtilis grown at temperatures below 37.degree. C contains 2 thymidylate synthetases, TSaseA and TSaseB. Their presence is dependent on functional thyA and thyB genes, respectively. When cells are grown at 46.degree. C they only contain TSaseA activity. This allows an easy positive selection for thyA and thyA,thyB mutants. The 2 TSases were physically separated, and they show similar overall requirements for activity. They differ significantly in both their kinetic and their physicochemical properties.