DNA uptake stimulating protein from Neurospora crassa enhances DNA and oligonucleotide uptake also in mammalian cells

The presence of the DNA uptake stimulating protein (designated earlier as DUSF by Schablik and Szabó (1981) FEMS Microbiol. Lett. 10, 395-397) was demonstrated on the surface of Neurospora crassa (FGSC 1118, slime) fungal cells as well as on HEp-2 and K562 human and F4N mouse tumor cells by immunofluorescence microscopy. DUSF markedly enhanced the uptake of both macromolecular [3H]DNA and of [3H]oligonucleotides by K562, HL-60 and also by DD human leukemia cells. Polyclonal anti-DUSF antibodies inhibited both the basal and stimulated [3H]oligonucleotide uptake by K562 cells. DNA-DNA hybridization has shown that the uptake of linearized pBR322 plasmid DNA into N. crassa and K562 cells was stimulated by DUSF, increasing proportionally with the length of incubation time. Unfragmented plasmid molecules were recovered from the cells. It is assumed that DUSF (or related proteins) may play a role in the physiological uptake of oligonucleotides and DNA not only in N. crassa but also in--at least some--mammalian cells.