Figure 4.

Categories of SIC and centromere configurations in short, linear Zip1 stretches. The different patterns of staining observed in Zip1 stretches containing one or two Zip2 or Zip3 foci are diagrammed, with the numbers observed indicated to the right of each category. Zip1 is indicated in blue, Ctf19/centromeres are in red, and Zip2 or Zip3 are in green. Zip1 stretches in category a differed in the degree of overlap between Zip1 and the Ctf19 focus: At one extreme, Zip1 and the Ctf19 focus overlapped only slightly, while at the other extreme, Zip1 staining extended all the way to the outside end of the Ctf19 focus. The same was true for the overlap between Zip1 and the Zip2 or Zip3 focus. It seems likely that these differences are artifacts of the spreading procedure; a Ctf19/Zip2/Zip3 focus located at one end of a Zip1 stretch may land in slightly different places relative to the Zip1 stretch when the three-dimensional object becomes compressed into two-dimensional space. In cases where Zip1 staining extended beyond the region of Ctf19 staining (a little or a lot), and Zip2 was located at the opposite end, then the stretch was placed in category b. Thus, some members of category b were difficult to distinguish from those in category a. Similarly, in category d, there was variation in the distance of the Zip2 focus from the end of the Zip1 stretch, and some stretches were only subtly different from those in category a. Similar logic and concerns apply to the assignment of Zip1 stretches in the other categories listed. For Zip2/Ctf19 localization, 44 nuclei were scored; for Zip3/Ctf19 localization, 19 nuclei were scored.