Volume 3

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

    134/952 (page 114)
    galK / 47.6 B 64.4 B -C att A 66.7 B ^bioB 0 B 80.0 B Figure 2.20: heteroduplex structure of F/F450. This defines the coordinate system used to describe the map of the sex factor, in which sites are described by distance in thousands of base pairs from the point 0/94.5 F. The bacterial DNA of the F' factor is described in the same way, but with a suffix B. Data of Sharp et al. (1972). other junction; thus when the same bacterial sequence is present on two different F' factors of independent origins, it may have different B coor dinates. In order to assign map locations to sequences on the sex factor, it is necessary to have reference points against which their positions can be measured. (Although the distance of a sequence from, for example, the insertion in F450 can be determined by forming a heteroduplex with this factor, this does not define a position unambiguously because it might lie on either side, clockwise or counterclockwise, of the insertion.) The structure of one of the reference factors, F8-33, that has been especially useful for heteroduplex mapping is illustrated in Figure 2.21. The F8-33 factor can be used to map virtually any F' factor because it has three distinctive structural features, comprising the small insertions c and d at 91.0 F and 35.2 F which are seen as deletion loops, and a bacterial insertion of 22,000 base pairs replacing the sex factor sequences from 8.5 to 16.3 F which is seen as a substitution loop. These features can be used