Biology subjects

Cecatiello, V.

Publications and source records attributed to Cecatiello, V..

3 recordsLinked to original sources

bioRxiv2026

Cryo-EM and single molecule visualization unravel the role of humancondensin II activation by M18BP1 in driving DNA compaction

DNA compaction by human condensin II is crucial for the correct organization of mitotic chromosomes. Mitotic activation of condensin II is a multi-layered process, controlled mainly by the opposing activity of the MCPH1 and M18BP1 proteins, acting as an interphase inhibitor and a mitotic activator, respectively. Mitotic phosphorylation favors M18BP1 binding to condensin II, resulting in effective and timely chromosome compaction. However, the molecular mechanisms underlying condensin II activation in driving DNA compaction remain uncharacterized. Combining cryo-electron microscopy with single molecule imaging we unravel the mechanism of condensin II activation by M18BP1 and elucidate their role in DNA compaction. The specific interaction with phosphorylated M18BP1 induces conformational changes in the condensin II complex, relieving an autoinhibitory conformation and thus allowing stable DNA binding and DNA compaction. Beyond the ATP-driven activity of isolated condensin II complexes on DNA, we observe the emergence of multimeric species that withstand the forces applied by optical tweezers, highlighting the contribution of condensin II protein-protein interactions to the mechanical reinforcement of mitotic chromosomes.

molecular biology↗

bioRxiv2024

Structural insights into distinct mechanisms of RNA polymerase II and III recruitment to snRNA promoters

RNA polymerase III (Pol III) is specialized in the transcription of short, essential RNAs, including the U6 small nuclear RNAs (snRNAs). At U6 snRNA genes, Pol III is recruited by the snRNA Activating Protein Complex (SNAPc) forming, together with a Brf2-containing TFIIIB complex, a transcriptionally competent pre-initiation complex (PIC). Additionally, SNAPc is responsible for the recruitment of Pol II at the remaining snRNAs genes (U1, 2, 4 and 5), representing a unique example of a multi subunit transcription factor shared among different RNA Polymerases. The mechanism of SNAPc cross-polymerase engagement and the role of the SNAPC2 and SNAPC5 subunits in transcription remain poorly defined. Here, we present cryo-EM structures of the full-length SNAPc-containing Pol III PIC assembled on the U6 snRNA promoter in the open and melting states at 3.2-4.2[A] resolution. Comparative structural analysis revealed unexpected differences with the yeast PIC and revealed the molecular basis of selective and structurally distinct SNAPc engagement within Pol III and Pol II PICs. Harnessing crosslinking mass spectrometry, we also localize the SNAPC2 and SNAPC5 subunits in proximity to the bound promoter DNA, expanding upon existing descriptions of snRNA Pol III PIC structure.

biochemistry↗

bioRxiv2024

Condensin II activation by M18BP1

Condensin complexes promote the drastic spatial rearrangement of the genome upon mitotic entry. Condensin II initiates chromosome condensation in early mitosis. To prevent chromosome condensation during interphase, condensin II is inhibited by MCPH1, but the mechanism is unknown. Through genetic and proteomic approaches, we identify M18BP1, a protein previously associated with centromere identity, as a factor required for condensin II localization to chromatin. M18BP1 directly binds condensin IIs CAP-G2 subunit and competes with MCPH1 for binding. Upon mitotic entry, CDK1 mediated phosphorylation may promote a switch from MCPH1 to M18BP1 binding to activate condensin II. Our results identify a fundamental and evolutionarily conserved mechanism of condensin II activation.

cell biology↗