Biology subjects

Fernandez Varela, P.

Publications and source records attributed to Fernandez Varela, P..

2 recordsLinked to original sources

bioRxiv2024

Restriction on Ku's Inward Translocation Caps Telomere Ends

Safeguarding chromosome ends against fusions via nonhomologous end joining (NHEJ) is essential for preserving genome integrity. Paradoxically, the conserved NHEJ core factor Ku binds telomere ends. How it is prevented from promoting NHEJ remains unclear, as does the mechanism that allows Ku to coexist with telomere-protective DNA binding proteins, e.g., Rap1 in Saccharomyces cerevisiae. Here, we reveal a direct role for Rap1 in the inhibition of Kus NHEJ function at telomeres. A single Rap1 molecule bound near a DNA end inhibits NHEJ in vivo without disrupting Ku presence. Consistent with this, Rap1 and Ku form a complex on short DNA duplexes in vitro. Cryo-EM and molecular modelling analysis of this complex shows that Rap1 obstructs Kus inward translocation on DNA - an essential step for NHEJ at broken ends. Nanopore sequencing of telomere fusions confirms the importance of this pathway in protecting native telomere ends. Collectively, our findings uncover a mechanism of telomere end protection mediated by restricting Kus inward translocation, a functional switch that prevents promiscuous NHEJ repair at telomeres.

molecular biology↗

bioRxiv2019

MglA functions as a three-state GTPase to control movement reversals of Myxococcus xanthus

In Myxococcus xanthus, directed movement is controlled by inter-dependent pole-to-pole oscillations of the small GTPase MglA, its GAP MglB and the RomR protein. However, these proteins have strikingly different oscillatory regimes such that MglA is segregated from MglB and RomR at reversal activation. The molecular mechanism whereby information is exchanged between the lagging and leading poles resulting in MglA detachment from the leading pole during reversals has remained unknown. Here, we show that MglA has two GTP-bound forms, one of which is insensitive to MglB (MglA-GTP*) and is re-sensitized to MglB by a feedback mechanism operated by MglA-GDP. By identifying the region of MglB that is critical for its association to the lagging pole, we demonstrate that MglA-GTP* is functional in vivo. These data suggest that MglA-GDP acts as a soluble messenger to convert polar MglA-GTP* into a diffusible MglA-GTP species, explaining MglA re-localization to the opposite pole during reversals.

microbiology↗