FIG 1.

Principle of the ANCHOR DNA labeling technology. (a) The ANCHOR system is composed of an ANCH DNA target sequence less than 1 kb long (red box) that specifically binds dimers of OR protein through nucleation sites. OR dimers spread on the DNA, and more OR dimers are recruited to form a large metastable nucleoprotein complex. When OR is fused to a fluorescent marker (green circles), accumulation of this complex on the ANCH sequence forms a spot that is easily detected by fluorescence microscopy. The ANCH sequence and a chimeric gene encoding the corresponding OR protein fused to a fluorescent protein may be associated in a cassette that can be inserted in a site-specific manner into the target viral genome, as shown in Fig. 2. (b) Representative image of a TB40-ANCHOR3-infected MRC5 cell 48 h p.i. showing accumulation of fluorescent spots in the nucleus (taken with a wide-field Zeiss Axiovert Observer Z1 with a 1.4-numerical-aperture [NA] 63× objective). Scale bar, 1 μm.