Fig. 4. Immunolocalisation of the p40/p50 protein on isolated chromosomes from C. tentans salivary gland cells. Polytene chromosomes were isolated and incubated with an affinity-purified p40/p50 antibody (A,B) or pre-immune serum (C,C' and D,D'), and subsequently incubated with a gold-conjugated secondary antibody. The immunogold labelling was silver-enhanced, and the specimens were photographed both in bright-field (A-F) and phase-contrast (C'-F') microscopy. Some chromosomes were RNase A treated before immunolabelling (E,E' and F,F'). A,A',C,C',E,E', chromosome IV; B,B',D,D'F,F', chromosome I. The three Balbiani rings (BR1-3) have been indicated in (A). Bar, 10 µm.