Plasmids constructed during the course of this work. pMS98 and pBF1 are derivatives of the plasmid pEY25, in which the φC31 int gene (blue arrow) is replaced with the SV1 g27 (encoding SV1 integrase; yellow arrow) and attP (red arrow) in orientations in which the SV1 g27 genes is being expressed from the tcp830 promoter (pBF1) or is orientated opposite to the tcp830 promoter (pMS98). pBF3 is a derivative of pMS98 in which the tcp830 promoter and the φC31 attR sites have been removed. The hygromycin resistance gene is represented by the pale red arrow and the tcp830 promoter by the green arrow. oriT is in grey.