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 b- 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.

EXAMPLE:

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.

Answer 1

14. From the above mentioned data, it is clear that the association of RSC with the nucleosome and DNA helps to form the nucleosome complex in the presence of ATP. With the increase in time, there is also an increase in the association of DNA with the histone core. But what kind of structure it is forming i.e. whether it is a 30nm structure or what kind of model they are forming is not clear from the experimental results. Hence it is difficult to identify whether there is any formation of solenoid structures. So the correct option is C.

15. Transcription initiation complex involves a lot of protein factors and importantly histones will not be associated during the transcription initiation. Dissociation of histones will lead to euchromatin structure. Our experimental data has shown that there is always an association of histones with DNA in the presence of RSC and ATP. The association has increased with time. But transcription initiation complex demands dissociation of histones from the DNA. So the correct option is B.