The function of RIII for TGF-β receptors is similar to that of the α subunit of the IL-2 receptor 

(means facilitating TGF-β binding to the RII and RI)

   

         

TLS Online TPP Program

#Id: 3990

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 3992

#Unit 2. Cellular Organization

Because nucleosomal DNA wraps around the histone protein 1.65 times, the formation of a single nucleosome using ccc plasmid would create a writhe of –1.65 and thus change the linking number by an equivalent amount. As described above, when the change in linking number associated with each nucleosome was measured, the number was lower than this, approximately –1.2 for each nucleosome added.

This discrepancy is referred to as the “nucleosome linking  number paradox,”

TLS Online TPP Program

#Id: 3993

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 3995

#Unit 2. Cellular Organization

When an ethidium ion intercalates between two base pairs, it causes the DNA to unwind by 260, reducing the normal rotation per base pair from 360 to 100. In other words, ethidium decreases the twist of DNA.

TLS Online TPP Program

#Id: 3997

#Unit 2. Cellular Organization

In a natural closed DNA that is negatively supercoiled, the intercalation of ethidium bromide first removes the negative supercoils and then introduces positive supercoils.

TLS Online TPP Program

#Id: 3998

#Unit 2. Cellular Organization

One approach is to measure the effect of nicking the DNA. Unconstrained supercoils are released by nicking, whereas constrained supercoils are unaffected. Nicking releases -50% of the overall supercoiling.

Another approach uses the crosslinking reagent psoralen, which binds more readily to DNA when it is under torsional tension. The reaction of psoralen with E. coli DNA in vivo corresponds to an average density of 1 negative super helical turn/200 bp (sigma = -0.05).