You are interested in examining the Psf gene.It is known that Psf is normally produced when cells are exposed to high levels of both calcium (Ca²⁺) and magnesium (Mg²⁺).MetA, MetB, and MetC are important for binding to the promoter of the Psf gene and are involved in regulating its transcription.MetA binds to the "A" site in the promoter region, MetB to the "B" site, and MetC to the "C" site.You create binding-site mutations in the A, B, and C sites and observe what happens to transcription of the Psf gene.Your results are summarized in Table Q8-12. $\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\underline{\text { Transcription in the presence of } \mathrm{Ca}^{2+} \text { and/or } \mathrm{Mg}^{2+}}$
$\begin{array}{lcccc}\text { Binding sites present } & \begin{array}{l}\text { No } \mathrm{Ca}^{2+} \\\text { or } \mathrm{Mg}^{2+}\end{array} & \begin{array}{l}\text { With } \\\mathrm{Ca}^{2+}\end{array} & \begin{array}{l}\text { With } \\\mathrm{Mg}^{2+}\end{array} & \begin{array}{l}\text { With } \mathrm{Ca}^{2+} \\\text { and } \mathrm{Mg}^{2 *}\end{array} \\\hline \text { A, B, and C } & - & - & - & ++ \\\hline \text { none } & - & - & - & - \\\hline \text { A only } & - & - & + & + \\\hline \text { B only } & - & - & - & - \\\hline \text { C only } & - & + & - & + \\\hline \text { A and B only } & - & - & - & + \\\hline \text { A and C only } & - & + & + & ++ \\\hline \text { B and C only } & - & - & - & +\end{array}$

$\text {For this table: -= no transcription of Pst,}$
$\text {\( += \) low level of transcription of Psf, and}$
$\text {\( ++= \) high levels of transcription of Pst.}$


Table 8-12
Which transcription factors are normally bound to the Psf promoter in the presence of both Mg²⁺ and Ca²⁺?