Question

The extent of condensation of chromatin plays an important role in the regulation of RNA transcription in eukaryotic cells. Chromatin-remodeling complexes are among proteins that control the physical state and functional activity of chromatin. The experiment described shortly was designed to study the role of a chromatin remodeling complex designated RSC (Remodeling the Structure of Chromatin) in the regulation of nucleosome dynamics. Figure 1 shows the results of an in vitro experiment. The reaction mixtures contained a 32-labelled 154 basepair long DNA fragment, un-labelled nucleosome core particles prepared from rat liver, purified RSC factor, and ATP. Reaction mixtures were incubated at 30C for the times indicated in the figure. Samples were then electrophoresed in a polyacrylamide gel under non-denaturing conditions, the gel was dried and visualized by autoradiography. Sample 6 contained a marker assembled by mixing the labelled 154 bp DNA fragment with nucleosomal histones. RSC + + + + + ATP + + + Incubation (min) 10 20 40 40 40 nucleosome - Sample 1 2 3 4 5 6 FIG. 1. In vitro analysis of the role of RSC in chromatin remodeling. For experimental details see the text. The arrow indicates the direction of electrophoresis. Figure Analysis: The following statements are related to the information presented in the description of the experiment. Based on the information given, select and again explain your answer. A if the statement is supported by the information given; B if the statement is contradicted by the information given; C if the statement is neither supported nor contradicted by the information given. 10. The RSC complex stimulates the release of histones from the nucleosomes. Rational: 11. _ The RSC complex stimulates the binding of nucleosomal histones to DNA.

Answer 1

ANSWER 10 :-

1. The Remodelling of structure of the chromatin (complex) stimulates the release of histones from the nucleolus. This statement should be correct. Lets consider the sample in lane 3 and lane 5. In this case, formation of a single band indicates that the histones are still assembled with the DNA indicating the importance of RSC complex in the release of histones leading to the formation of two separate bands highlighted in lane 3 in the presence of RSC.
2. So, option A is the most appropriate answer.

ANSWER 11 :-

1. Binding of the nucleosomal histones to the DNA is being supported by the RSC complex and this statement is correct. The complex basically is dependent on ATP molecule for its activity and the absence of ATP molecule would directly alter the progression as it will alter the binding of histones to the DNA indicating the inefficiency of the RSC to mediate the binding or interaction between the negatively charged DNA and the positively charged Histone proteins. As can be seen in lane 3 and lane 4, there is a major difference. Lane 3 shows that ATP is present in the reaction mixture and absent in case of lane 4 due to which the activity is stopped as can be seen from a single band in case of lane 4.
2. So, option A should be the most appropriate answer.

ANSWER 12 :-

1. From the above mentioned data, the significance of ATP molecule in the event progression is seen although taking into consideration that the process is carried out in an in-vitro manner, the possibility of transcription occuring decreases taking into consideration the errors associated with the changes in certain conditions associated with the experimental setup and hence it becomes difficult to identify if there is actual phosphorylation occuring of the nucleosomal histone proteins. This in other terms cannot be viewed or analysed through basic electrophoretic techniques and hence it can neither ne considered contradictory nor a supporting statement taking into consideration the information.
2. Hence, option C is the most appropriate answer.

ANSWER 13 :-

1. From the above mentioned data, it is clear that the RSC is associated with release of histones and binding of histones to the DNA although the prior step is that is possibly not true is the stabilization of the nucleosomal structure by the RSC. From the gel electrophoresis data, one can state that the process of stabilization is not occuring as various mechanisms may play a vital in the stabilization of protein structure such as a phosphorylation event which is not highlighted in this process indicating that the RSC is not involved in stabilization.
2. Hence, option B should be the most appropriate answer.

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