title: DNA binding and unwinding activities associated with intracytoplasmic a particles isolated from mouse mammary tumors.
abstract: Intracytoplasmic A particles (CAP), previously identified as probably 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 sulphate (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.
mesh_terms: D000818:Animals; D002213:Capsid / Q000276:immunology / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D005260:Female; D015683:Gene Products, gag; D007985:Leydig Cells; D008297:Male; D008325:Mammary Neoplasms, Experimental / Q000382:microbiology; D008324:Mammary Tumor Virus, Mouse / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D009374:Neoplasms, Experimental / Q000382:microbiology; D013736:Testicular Neoplasms / Q000382:microbiology; D014764:Viral Proteins / Q000276:immunology / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D015683:Gene Products, gag; D014764:Viral Proteins; D004247:DNA; D004265:DNA Helicases