Fig. 3. Cohesin associates with the cut locus in salivary gland chromosomes. (A) Wild-type (Oregon R) polytene chromosomes double immunostained for the Smc1 (green) and Stromalin (red) cohesin subunits. The merged image shows that both subunits bind the same sites. Identities of the chromosome arms are indicated in the phase-contrast micrograph. The staining pattern is reproducible in several spreads. Neither pre-immune serum showed staining, and the secondary antibodies did not show cross-species reactivity. (B) Higher magnification of the anti-Stromalin staining (red), showing cohesin association with the 7B3-4 region (arrows) containing cut. The phase-contrast micrograph is a photographic negative to make it easier to see cohesin staining in the merge.