Ahel et al. show that the ChAHP complex drives SINE B2 repression independently of HP1 and not through steric occlusion. Instead, CHD4-dependent chromatin-remodeling activity repositions nucleosomes, ...

Short interspersed nuclear elements (SINEs) are abundant non-autonomous transposable elements derived from RNA polymerase III (POL III)-transcribed short non-coding RNAs. SINEs retain sequence feature...

Short interspersed nuclear elements (SINEs) are abundant non-autonomous transposable elements derived from RNA polymerase III (POL III)-transcribed short non-coding RNAs. SINEs retain sequence features recognized by the POL III machinery and constitute a substantial portion of vertebrate genomes. Despite their impact on genome stability and evolution, the mechanisms governing SINE transcription remain poorly understood. Although DNA methylation and heterochromatin formation have been implicated in their repression, we find these pathways play only a minor role in mouse embryonic stem cells. Instead, we identify the ChAHP complex as a key repressor of SINE B2 elements. ChAHP directly inhibits POL III transcription by blocking TFIIIB recruitment without affecting TFIIIC binding. This selective interference prevents transcription initiation and highlights a distinct regulatory mechanism. Our findings establish ChAHP as a non-canonical repressor of POL III-dependent SINE transcription, offering new insights into the control of this pervasive class of non-coding genomic elements. ### Competing Interest Statement The Friedrich Miescher Institute for Biomedical Research (FMI) receives significant financial contributions from the Novartis Research Foundation. Published research reagents from the FMI are shared with the academic community under a Material Transfer Agreement (MTA) having terms and conditions corresponding to those of the UBMTA (Uniform Biological Material Transfer Agreement). Novartis Research Foundation, n.a. Swiss National Science Foundation, grant 10.001.858 EMBO Postdoctoral Fellowship, ALTF 705-2021

Transcription in eukaryotes is regulated by chromatin-based mechanisms that control nucleosome occupancy, chromatin modifications, and transcription factor binding. We have previously shown that the transcription factor ADNP forms the ChAHP complex with the chromatin remodeler CHD4 and HP1 proteins, acting as a site-specific regulator of transcription and antagonist of CTCF binding. However, the molecular basis of these functions remained unclear. Here, we demonstrate that the CHD4 subunit is essential to antagonize CTCF and silence transcription of transposons, while HP1 proteins are dispensable. Although the remodeling activity of CHD4 is not required for ChAHP chromatin association, it is critical for both transposon repression and CTCF antagonism. Our findings support a model wherein ADNP recruits chromatin remodeling activity in a sequence-specific manner, enabling transcriptional control and local modulation of chromatin architecture. ### Competing Interest Statement The Friedrich Miescher Institute for Biomedical Research (FMI) receives significant financial contributions from the Novartis Research Foundation. Published research reagents from the FMI are shared with the academic community under a Material Transfer Agreement (MTA) having terms and conditions corresponding to those of the UBMTA (Uniform Biological Material Transfer Agreement). Novartis Research Foundation, n.a. Swiss National Science Foundation, grant 310030_188835

Transcription in eukaryotes is regulated by chromatin-based mechanisms that control nucleosome occupancy, chromatin modifications, and transcription factor binding. We have previously shown that the transcription factor ADNP forms the ChAHP complex with the chromatin remodeler CHD4 and HP1 proteins, acting as a site-specific regulator of transcription and antagonist of CTCF binding. However, the molecular basis of these functions remained unclear. Here, we demonstrate that the CHD4 subunit is essential to antagonize CTCF and silence transcription of transposons, while HP1 proteins are dispensable. Although the remodeling activity of CHD4 is not required for ChAHP chromatin association, it is critical for both transposon repression and CTCF antagonism. Our findings support a model wherein ADNP recruits chromatin remodeling activity in a sequence-specific manner, enabling transcriptional control and local modulation of chromatin architecture. ### Competing Interest Statement The Friedrich Miescher Institute for Biomedical Research (FMI) receives significant financial contributions from the Novartis Research Foundation. Published research reagents from the FMI are shared with the academic community under a Material Transfer Agreement (MTA) having terms and conditions corresponding to those of the UBMTA (Uniform Biological Material Transfer Agreement). Novartis Research Foundation, n.a. Swiss National Science Foundation, grant 310030_188835

Short interspersed nuclear elements (SINEs) are abundant non-autonomous transposable elements derived from RNA polymerase III (POL III)-transcribed short non-coding RNAs. SINEs retain sequence features recognized by the POL III machinery and constitute a substantial portion of vertebrate genomes. Despite their impact on genome stability and evolution, the mechanisms governing SINE transcription remain poorly understood. Although DNA methylation and heterochromatin formation have been implicated in their repression, we find these pathways play only a minor role in mouse embryonic stem cells. Instead, we identify the ChAHP complex as a key repressor of SINE B2 elements. ChAHP directly inhibits POL III transcription by blocking TFIIIB recruitment without affecting TFIIIC binding. This selective interference prevents transcription initiation and highlights a distinct regulatory mechanism. Our findings establish ChAHP as a non-canonical repressor of POL III-dependent SINE transcription, offering new insights into the control of this pervasive class of non-coding genomic elements. ### Competing Interest Statement The Friedrich Miescher Institute for Biomedical Research (FMI) receives significant financial contributions from the Novartis Research Foundation. Published research reagents from the FMI are shared with the academic community under a Material Transfer Agreement (MTA) having terms and conditions corresponding to those of the UBMTA (Uniform Biological Material Transfer Agreement). Novartis Research Foundation, n.a. Swiss National Science Foundation, grant 10.001.858 EMBO Postdoctoral Fellowship, ALTF 705-2021