One dominant polygene contribute=Max phenotype – Min phenotype

                                                              Number of dominant polygene in      

                                                               maximum phenotype

TLS Online TPP Program

#Id: 3985

#Unit 2. Cellular Organization

Gyrases are A2B2 heterotetramers in which the B subunits bind and hydrolyze ATP and the A subunits mediate the double-strand cleavage, strand passage, and reunion reactions.

The eukaryotic type II topoisomerases are homologous to gyrases but with their A and B subunits fused so that they are homodimers.

TLS Online TPP Program

#Id: 3986

#Unit 2. Cellular Organization

Addition of a topoisomerase greatly facilitates nucleosome association with cccDNA.

When a topoisomerase is present during nucleosome assembly, it cannot act on the DNA bound to the nucleosome. Instead, the topoisomerase relaxes the DNA not included in nucleosomes, reducing the positive superhelical density in these regions by decreasing the linking number.

TLS Online TPP Program

#Id: 3988

#Unit 2. Cellular Organization

By maintaining the unbound DNA in a relaxed state, topoisomerases facilitate the binding of histones to the DNA and the formation of additional nucleosomes.

Importantly, the overall effect on the plasmid is that the linking number is decreased as more nucleosomes are assembled

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