## 3 Results and Discussion
### Quantitative Identification of 11 Hypersensitive Strains  
Chemogenetic screening provides an additional advantage of measuring the growth kinetics over constant intervals of time [29]. As many heterozygous mutants grow slowly in culture medium, it is necessary to compare the growth kinetics of treated and untreated mutants and wildtype [22]. _S. cerevisiae_ mutants lacking specific protein function were employed to assess the hypersensitive strains compared to wildtype. In the present study, 11 yeast mutants were recognized as hypersensitive compared to the untreated strains (Table 1). Mutants \(\Delta yap1\), \(\Delta glr1\), \(\Delta zwfl\), \(\Delta trx2\) and \(\Delta gnd1\) were then studied in more detail. These five yeast mutants were chosen for detailed analysis because these mutants lack genes coding for proteins implicated in glutathione metabolism, and proteins for oxidative stress tolerance. These mutants are deficient in genes sharing a common pathway. The other mutants hypersensitive to selenocyanates might also point towards the role of proteins other than those of glutathione metabolism and oxidative stress tolerance. The ability of wildtype (wt) BY4742 cells to grow in the presence of selenocyanate was compared with the ability of \(\Delta yap1\), \(\Delta glr1\), \(\Delta zwfl\), \(\Delta gnd1\) and \(\Delta trx2\) yeast mutants. The redox controlled transcription factor Yap1p plays central role in the regulation of the oxidative stress response in yeast [37]. Yap1 regulates the expression of numerous oxidative stress tolerance, glutathione metabolism and detoxifying genes, such as _GSH1_, _GSH2_, _TRX2_ and _GLR1_[38,39]. Glr1p reduces GSSG to GSH by utilizing NADPH. Trx2p is the main thioredoxin in yeast which reduces glutathionealted proteins (PSSG) and disulfides (PSSP) back to thiols utilizing NADPH-dependent thioredoxin reductases [40]. NADPH is predominantly produced by glucose-6-phosphate dehydrogenase (Zwflp) and 6-phosphogluconate dehydrogenase (Gnd1p) in the oxidative pentose phosphate pathway (PPP) [30]. Thus, these mutants point towards the glutathione metabolism as common mode of action of two selenocyanates. As a precondition, the treatment of yeast with compound in question must cause the inhibition of growth. Figure 2 shows the growth inhibition of BY4742 against different concentrations of selenocyanates. The two compounds inhibited the growth of wildtype (BY4742) in shake cultures in concentration dependent manner. Compound **2** completely inhibited the growth of wt at concentration \(\geq\)20 \(\upmu\)M. However, compound **1** exhibited maximum toxicity at concentration of 30 \(\upmu\)M. These results reveal the involvement of genes required for specific functions; e.g., glutathione metabolism and oxidative stress resistance. \begin{table}
\begin{tabular}{c c c} \hline \hline
**ORF** & **Gene** & **Biological/Molecular Function** \\ \hline _YNL241C_ & _ZWF1_ & glucose-6-phosphate dehydrogenase activity \\ _YML007W_ & _YAP1_ & DNA-binding transcription factor activity \\ _YPL091W_ & _GLR1_ & glutathione-disulfide reductase activity \\ _YGR209C_ & _TRX2_ & disulfide oxidoreductase activity \\ _YHR183W_ & _GND1_ & phosphogluconate dehydrogenase (decarboxylolating) activity \\ _YOR375C_ & _GDH1_ & glutamate dehydrogenase (NADP+) activity \\ _YDL085W_ & _NDE2_ & NADH dehydrogenase activity \\ _YDR197W_ & _CBS2_ & translation regulator activity \\ _YJR009C_ & _TDH2_ & glyceraldehyde-3-phosphate dehydrogenase (NAD+) activity \\ _YGR234W_ & _YHB1_ & nitric oxide reductase activity \\ _YML056C_ & _IMD4_ & IMP dehydrogenase activity \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Names and functions of genes mutated in strains showing hypersensitivity as compared to the wildtype against compounds **1** and **2**.