Two domains of Tim50 coordinate translocation of proteins across the two mitochondrial membranes.

Hundreds of mitochondrial proteins with N-terminal presequences are translocated across the outer and inner mitochondrial membranes via the TOM and TIM23 complexes, respectively. How translocation of proteins across two mitochondrial membranes is coordinated is largely unknown. Here, we show that the two domains of Tim50 in the intermembrane space, named core and PBD, both have essential roles in this process. Building upon the surprising observation that the two domains of Tim50 can complement each other in trans, we establish that the core domain contains the main presequence-binding site and serves as the main recruitment point to the TIM23 complex. On the other hand, the PBD plays, directly or indirectly, a critical role in cooperation of the TOM and TIM23 complexes and supports the receptor function of Tim50. Thus, the two domains of Tim50 both have essential but distinct roles and together coordinate translocation of proteins across two mitochondrial membranes.

The BRCA2 and CDKN1A-interacting protein (BCCIP) stabilizes stalled replication forks and prevents degradation of nascent DNA.

DNA replication stress is characterized by impaired replication fork progression, causing some of the replication forks to collapse and form DNA breaks. It is a primary cause of genomic instability leading to oncogenic transformation. The repair-independent functions of the proteins RAD51 and BRCA2, which are involved in homologous recombination (HR)-mediated DNA repair, are crucial for protecting nascent DNA strands from nuclease-mediated degradation. The BRCA2 and CDKN1A-interacting protein (BCCIP) associates with BRCA2 and RAD51 during HR-mediated DNA repair. Here, we investigated the role of BCCIP during the replication stress response. We find that in the presence of replication stress, BCCIP deficiency increases replication fork stalling and results in DNA double-strand break formation. We show that BCCIP is recruited to stalled replication forks and prevents MRE11 nuclease-mediated degradation of nascent DNA strands.