Telomerase-associated protein 1, HSP90, and topoisomerase IIalpha associate directly with the BLM helicase in immortalized cells using ALT and modulate its helicase activity using telomeric DNA substrates.

The BLM helicase associates with the telomere structural proteins TRF1 and TRF2 in immortalized cells using the alternative lengthening of telomere (ALT) pathways. This work focuses on identifying protein partners of BLM in cells using ALT. Mass spectrometry and immunoprecipitation techniques have identified three proteins that bind directly to BLM and TRF2 in ALT cells: telomerase-associated protein 1 (TEP1), heat shock protein 90 (HSP90), and topoisomerase IIalpha (TOPOIIalpha).

Deriving mouse spermatogonial stem cell lines.

In adult males, spermatogonial stem cells function to replenish developing gametes that are continuously released from the testes as mature spermatozoa. Because of their potential importance to research, medicine, industry, and conservation, numerous attempts have been made in the past to cultivate sperma-togonial stem cells in vitro. However, only recently have culture methods been established that effectively promote the proliferation of mammalian spermatogonial stem cells in vitro.

BLM helicase complements disrupted type II telomere lengthening in telomerase-negative sgs1 yeast.

Recombination-mediated pathways for telomere lengthening may be utilized in the absence of telomerase activity. The RecQ-like helicases, BLM and Sgs1, are implicated in recombination-mediated telomere lengthening in human cells and budding yeast, respectively. Here, we show that BLM expression rescues disrupted telomere lengthening in telomerase-negative sgs1 yeast.

Association and regulation of the BLM helicase by the telomere proteins TRF1 and TRF2.

In addition to increased DNA-strand exchange, a cytogenetic feature of cells lacking the RecQ-like BLM helicase is a tendency for telomeres to associate. We also report additional cellular and biochemical evidence for the role of BLM in telomere maintenance. BLM co-localizes and complexes with the telomere repeat protein TRF2 in cells that employ the recombination-mediated mechanism of telomere lengthening known as ALT (alternative lengthening of telomeres).