BLM protein is located in the nucleus of normal human cells in the nuclear domain 10 (ND10) or promyelocytic leukemia nuclear bodies. These structures are punctate deposits of proteins disrupted upon viral infection and in certain human malignancies.

BLM was found primarily in ND10 except during S phase, when it colocalized with the WRN gene product, in the nucleolus. BLM colocalized with a select subset of telomeres in normal cells and with large telomeric clusters seen in simian virus 40-transformed normal fibroblasts. During S phase, Bloom syndrome cells expel micronuclei containing sites of DNA synthesis. The BLM protein is likely to be part of a DNA surveillance mechanism operating during S phase.