1). What portion of the nucleoplasmin molecule is responsible for localization i
ID: 188498 • Letter: 1
Question
1). What portion of the nucleoplasmin molecule is responsible for localization in the nucleus?PART B-Data handling 3) Before nuclear pore complexes were well nucleoplasmin nuclear cytoplasmic understood. It was unclear whether nuclear preparation injection injection proteins diffused passively into the nucleus and accumulated there by binding to intact residents of the nucleus such as chromosomes, or whether they were actively imported and accumulated regardless of their affinity for nuclear components. one tail A classic experiment that addressed this problem used several forms of radioactive nucleoplasmin, which is a large pentameric protein involved in chromatin assembly. In this experiment, either the intact protein or the nucleoplasmin heads, tails or heads with a single tail were injected into the cytoplasm of a frog oocyte or into the nucleus (Figure 1). All forms of nucleoplasmin, except heads, accumulate in the nucleus when injected into the cytoplasm, and all forms were retained in nucleoplasmin and nucleoplasmin the nucleus when injected there. heads only tails only ) C Figure 1: Cellular location of injected components. Schematic diagrams of autoradiographs show the cytoplasm and nucleus with the localization of nucleoplasmin (red). 1. What portion of the nucleoplasmin molecule is responsible for localization in the nucleus? 2. How do these experiments distinguish between active transport, in which a nuclear localization signal triggers transport by the nuclear pore complex, and passive diffusion, in which a binding site for a nuclear component allows accumulation in the nucleus?
Explanation / Answer
Answer:
1. The portion of nucleoplasmin responsible for localization in the nucleus must reside in the tail. The nucleoplasmin head does not localize to the nucleus when injected into the cytoplasm, and it is the only injected component that is missing a tail.
2. These experiments suggest that the nucleoplasmin tail carries a nuclear localization signal and that accumulation in the nucleus is not the result of passive diffusion. The observations involving complete nucleoplasmin or fragments that retain the tail do not distinguish between passive diffusion and active transport; they suggest that the tail carries the important part of nucleoplasmin - be it a localization signal or a binding site.
The key observations that argue against passive diffusion are the results with the nucleoplasmin heads. They do not diffuse into the cytoplasm when they are injected into the nucleus, nor into the nucleus when injected into the cytoplasm, suggesting that the heads are too large to pass through the nuclear pores. Since the more massive forms of nucleoplasmin with tails do pass through the nuclear pores, passive diffusion of nucleoplasmin is ruled out.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.