FIGURE 4.

Competition for cpSRP43 binding to the C terminus of Alb3 in salt-washed thylakoids. Salt-washed thylakoids (equivalent to 75 μg of chlorophyll) and 8 nmol of recombinant cpSRP43 construct as indicated were incubated for 15 min at 25 °C in light. Equal amounts of radiolabeled cpSRP43 were added to each tube and incubated an additional 30 min under the same conditions. Samples were pelleted, washed, and analyzed via SDS-PAGE and phosphorimaging for radiolabeled cpSRP43. The graph depicts the amount of radiolabeled cpSRP43 bound to salt-washed thylakoids relative to the amount recovered when no recombinant protein was added. It has been previously demonstrated that cpSRP43 binding to salt-washed thylakoids takes place through a cpSRP43/Alb3-Cterm interaction (2). As shown, all of the ankyrin region-containing constructs (including cpSRP43 lacking CD2CD3) were able to prevent cpSRP43 binding to the C terminus of Alb3 in salt-washed thylakoids whereas chromodomains 1, 2, and 3 did not prevent cpSRP43 binding to thylakoids.