Polλ promotes microhomology-mediated end-joining.

The double-strand break (DSB) repair pathway called microhomology-mediated end-joining (MMEJ) is thought to be dependent on DNA polymerase theta (Polθ) and occur independently of nonhomologous end-joining (NHEJ) factors. An unresolved question is whether MMEJ is facilitated by a single Polθ-mediated end-joining pathway or consists of additional undiscovered pathways. We find that human X-family Polλ, which functions in NHEJ, additionally exhibits robust MMEJ activity like Polθ.

Publisher Correction: Molecular basis of microhomology-mediated end-joining by purified full-length Polθ.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Molecular basis of microhomology-mediated end-joining by purified full-length Polθ.

DNA polymerase θ (Polθ) is a unique polymerase-helicase fusion protein that promotes microhomology-mediated end-joining (MMEJ) of DNA double-strand breaks (DSBs). How full-length human Polθ performs MMEJ at the molecular level remains unknown. Using a biochemical approach, we find that the helicase is essential for Polθ MMEJ of long ssDNA overhangs which model resected DSBs.

Polymerase θ-helicase efficiently unwinds DNA and RNA-DNA hybrids.

is a unique multifunctional replication and repair gene that encodes for a N-terminal superfamily 2 helicase and a C-terminal A-family polymerase. Although the function of the polymerase domain has been investigated, little is understood regarding the helicase domain. Multiple studies have reported that polymerase θ-helicase (Polθ-helicase) is unable to unwind DNA.

Mechanism of microhomology-mediated end-joining promoted by human DNA polymerase θ.

Microhomology-mediated end-joining (MMEJ) is an error-prone alternative double-strand break-repair pathway that uses sequence microhomology to recombine broken DNA. Although MMEJ has been implicated in cancer development, the mechanism of this pathway is unknown. We demonstrate that purified human DNA polymerase θ (Polθ) performs MMEJ of DNA containing 3' single-strand DNA overhangs with ≥2 bp of homology, including DNA modeled after telomeres, and show that MMEJ is dependent on Polθ in human cells.

Changes in PINCH levels in the CSF of HIV+ individuals correlate with hpTau and CD4 count.

Several studies report associations between the particularly interesting new cysteine histidine-rich (PINCH) protein and HIV-associated CNS disease. PINCH is detected in the CSF of HIV patients, and changes in levels during disease may be indicative of changes in disease status over time. PINCH binds hyperphosphorylated Tau (hpTau) in the brain and CSF, but little is known about the relevance of these interactions to HIV CNS disease.

PINCH in the cellular stress response to tau-hyperphosphorylation.

Particularly interesting new cysteine- histidine- rich protein (PINCH) is an adaptor protein that our data have shown is required for neurite extension under stressful conditions. Our previous studies also report that PINCH is recalled by neurons showing decreased levels of synaptodendritic signaling proteins such as MAP2 or synaptophysin in the brains of human immunodeficiency virus (HIV) patients. The current study addressed potential role(s) for PINCH in neurodegenerative diseases.