ABSTRACT The eukaryotic genome is packaged into chromatin, which limits the accessibility of RNA polymerase during transcription. Recent finding in metazoan systems have revealed that much of the transcription regulation occurs downstream of recruitment of the polymerase, through modulation of pausing and the efficiency of early elongation (Adelman and Lis, 2012). Although we have learned some of the molecular players that modulate escape from promoter proximal pausing, whether chromatin accessibility and which chromatin modifiers modulate this process, remains to be fully understood. Remarkably, we have recently identified the histone deacetylase SIRT6 as a central regulator of embryonic differentiation and metabolism, modulating expression of key developmental and metabolic genes to adapt against nutrient stress (Mostoslavsky et al., 2006; Zhong et al., 2010; Etchegaray et al., 2015); furthermore, SIRT6 acts as a tumor suppressor, inhibiting cancer metabolism amd Myc-dependent transcription (Sebastian et al., 2012; Kugel et al., 2015; Kugel et al., 2016). These studies indicate that fine-tuning of gene expression by SIRT6 is key to maintain cellular homeostasis. In this proposal, we will test the innovative idea that SIRT6 acts downstream of recruitment of the polymerase to modulate promoter proximal pausing, a novel, previously unidentified mechanism of regulation for an histone deacetylase. Specifically, we will 1) Determine, at the molecular level, the function of SIRT6 in transcriptional elongation 2) Decipher, biochemically, whether SIRT6 controls elongation using defined, fully reconstituted in-vitro systems and biochemical assays to test transcriptional elongation in chromatinized templates. 3) Determine the physiological relevance for SIRT6 roles in transcriptional elongation during early embryonic development. Overall, our results should provide new insights into the molecular mechanisms of transcriptional regulation, in particular those related to early development and adaptive responses to metabolic cues, a knowledge that may inform treatment against developmental diseases, metabolic diseases and cancer.