DNA binding and unwinding activities associated with intracytoplasmic A particles isolated from mouse mammary tumours

G. H. Smith, M. A. Mirski, L. O. Arthur

Research output: Contribution to journalArticle


Intracytoplasmic A particles (CAP), previously identified as probable cytoplasmic nucleocapsid precursor structures to mouse mammary tumour virus (MMTV), possess both DNA binding and DNA unwinding activities. CAP proteins bind to both single-stranded (ss)- and double-stranded (ds)DNA, with the ssDNA slightly preferred. This activity was linear over a 30-fold concentration of A particle protein and was not affected by NaCl concentrations as high as 0.6 M or pH changes over a wide range. DNA binding by CAP proteins was sensitive to heat or addition of sodium dodecyl sulfate (SDS) and was neutralized by pre-incubation of CAP with anti-MMTV p14, but not by anti-MMTV p27, p10 or anti-mouse casein. Incubation of CAP with dsDNA led to unwinding of the double helix as measured by its increased sensitivity to S1 nuclease digestion. This activity was also linear over a several-fold concentration of A particle protein and was heat labile. It was not inhibited by pre-incubation of CAP with either anti-MMTV p14 or with anti-MMTV, anti-MMTV p27 and anti-MMTV p10. DNA unwinding was inhibited by anti-A particle antiserum and to a lesser extent by anti-CAP p20-18.

Original languageEnglish (US)
Pages (from-to)263-272
Number of pages10
JournalJournal of General Virology
Issue number2
StatePublished - Jan 1 1980


ASJC Scopus subject areas

  • Virology

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