Passage
Quantitative fluorescence recovery after photobleaching (FRAP) is used to study the movement of molecules in live cells. During FRAP, the fluorescence of a green fluorescent protein (GFP) -tagged molecule is first measured and then photodestroyed in targeted cell regions. Researchers then assess the time course for fluorescence recovery, which is an indicator of molecular mobility of the GFP-tagged protein into the photodestroyed region. The average time required to recover 80% of the pre-bleach fluorescence of protein histone 1 (H1) fused to GFP (H1-GFP) in the photodestroyed region is given as t80.FRAP was used to analyze the mobility of the architectural H1 alone and in the presence of high-mobility group (HMG) proteins. HMG proteins are dynamic modifiers that have been shown to have opposite effects but similar binding sites on chromatin structure.
Figure 1 Unique chromatin binding motifs of HMG proteinsDuring analysis, HMGA1 and HMGB1 were microinjected into the cytoplasm of mouse embryonic fibroblast cells expressing H1-GFP. FRAP was performed on euchromatin and heterochromatin. Euchromatin and heterochromatin domains were identified as regions weakly and strongly stained by H1-GFP, respectively. The relative intensity of H1-GFP fluorescence in euchromatin and heterochromatin of uninjected and injected cells was assessed, and t80 results are shown in Table 1.Table 1 Effect of HMGB1 and HMGA1 on H1-GFP Mobility
Adapted from Catez F, Yang H, Tracey KJ, Reeves R, Misteli T, Bustin M. Network of dynamic interactions between histone H1 and high-mobility-group proteins in chromatin. Mol Cell Biol. 2004;24(10) :4321-8.
-Based on Figure 1, HMGN2 is most likely to interact with a histone complex that is rich in:

Question

Passage
Quantitative fluorescence recovery after photobleaching (FRAP) is used to study the movement of molecules in live cells. During FRAP, the fluorescence of a green fluorescent protein (GFP) -tagged molecule is first measured and then photodestroyed in targeted cell regions. Researchers then assess the time course for fluorescence recovery, which is an indicator of molecular mobility of the GFP-tagged protein into the photodestroyed region. The average time required to recover 80% of the pre-bleach fluorescence of protein histone 1 (H1) fused to GFP (H1-GFP) in the photodestroyed region is given as t80.FRAP was used to analyze the mobility of the architectural H1 alone and in the presence of high-mobility group (HMG) proteins. HMG proteins are dynamic modifiers that have been shown to have opposite effects but similar binding sites on chromatin structure.

Figure 1 Unique chromatin binding motifs of HMG proteinsDuring analysis, HMGA1 and HMGB1 were microinjected into the cytoplasm of mouse embryonic fibroblast cells expressing H1-GFP. FRAP was performed on euchromatin and heterochromatin. Euchromatin and heterochromatin domains were identified as regions weakly and strongly stained by H1-GFP, respectively. The relative intensity of H1-GFP fluorescence in euchromatin and heterochromatin of uninjected and injected cells was assessed, and t80 results are shown in Table 1.Table 1 Effect of HMGB1 and HMGA1 on H1-GFP Mobility

Adapted from Catez F, Yang H, Tracey KJ, Reeves R, Misteli T, Bustin M. Network of dynamic interactions between histone H1 and high-mobility-group proteins in chromatin. Mol Cell Biol. 2004;24(10) :4321-8.
-Based on Figure 1, HMGN2 is most likely to interact with a histone complex that is rich in:

Quizplus · Accepted Answer

11ecba2d_0f3a_5b88_a3bf_3f1a19325365_MD0008_00 Based on the passage, the protein HMGN2 contains a nucleosomal binding domain, meaning that it most likely interacts with a nucleosome. During the initial steps of DNA packaging in the cell nucleus, the DNA double helix wraps twice around a histone octamer (eight-protein complex) to form a structural subunit known as the nucleosome. H1, H2A, H2B, H3, and H4 are the five major histone types, but the DNA-wrapped octamer core is composed of eight subunits (ie, two molecules each of H2A, H2B, H3, and H4). These histone proteins have a net positive charge at physiological pH because they are rich in arginine and lysine (positively charged, basic amino acids). This net positive charge facilitates histone binding to negatively charged DNA. (Choices A, B and C) Molecules with opposing charges attract each other, but those with like charges repel each other. Aspartate and glutamate are negatively charged amino acids and therefore would impede (ie, repel) binding to the DNA double helix, which is also negatively charged. As a result, any molecule rich in either of these two negatively charged amino acids would not be able to bind negatively charged DNA. Educational objective: The nucleosome is a structural subunit composed of DNA wrapped twice around a histone octamer, which contains two molecules of H2A, H2B, H3, and H4. H1 is located outside the octamer core and serves as the "linker" protein that secures the DNA wrapped around the nucleosome. Histone proteins are rich in positively charged arginine and lysine, which facilitate binding to negatively charged DNA.

Passage Quantitative Fluorescence Recovery After Photobleaching (FRAP) Is Used to Study