To study the relevance of the phosphorylation of Spt4 in residues T42 and S43, we assessed the genome-wide transcriptional response of the non-phosphorylatable Spt4-T42A/S43A mutant (Spt4-AA) upon osmotic stress. Results point out that the unphosphorylatable Spt4-T42A/S43A protein showed an impaired stress responsive gene expression indicating that these specific residues play a relevant role in osmotic stress responsive transcriptional regulation. Overall design: Total RNA obtained from the Saccharomyces cerevisiae BY4741 Spt4-TAP (WT) or BY4741 Spt4-T42A/S43A-TAP mutant (Spt4-AA) untreated or subjected to osmotic stress (15 min at 0.4M NaCl). Experiment was done by triplicate.