These genes encode proteins of the COP1–SUPPRESSOR OF PHYA (COP1–SPA) complex, the COP9 signalosome (CSN) complex.

TLS Online TPP Program

#Id: 5886

#Unit 3. Fundamental Processes

The DNA polymerase monitors the ability of the incoming nucleotide to form an A:T or G:C base pair, rather than detecting the exact nucleotide that enters the active site in a DNA polymerase with significantly reduced discrimination

between dNTPs and rNTPs.

TLS Online TPP Program

#Id: 5887

#Unit 3. Fundamental Processes

Only when a correct base pair is formed are the 3’-OH of the primer and the a-phosphate of the incoming nucleoside triphosphate in the optimum position for catalysis to occur.

TLS Online TPP Program

#Id: 5888

#Unit 3. Fundamental Processes

Incorrect base pairing leads to dramatically lower rates of nucleotide addition as a result of a catalytically unfavorable alignment of these substrates. This is an example of kinetic proofreading, in which an enzyme favors catalysis using one of several possible substrates by dramatically increasing the rate of bond formation only when the correct substrate is present. 

TLS Online TPP Program

#Id: 5889

#Unit 3. Fundamental Processes

DNA polymerases show an impressive ability to distinguish between ribonucleoside and deoxyribonucleoside triphosphates (rNTPs 10 and 1 dNTPs)

TLS Online TPP Program

#Id: 5890

#Unit 3. Fundamental Processes

In DNA polymerase, the nucleotide-binding pocket cannot accommodate a 2’-OH on the in-coming nucleotide. This space is occupied by two amino acids that make van der Waals contacts with the sugar ring. Changing these amino acids to other amino acids with 

TLS Online TPP Program

#Id: 5891

#Unit 3. Fundamental Processes

DNA binds in a large cleft composed of three domains. The “palm” domain has important conserved sequence motifs that provide the catalytic active site. The “fingers” are involved in positioning the template correctly at the active site. The “thumb” binds the DNA as it exits the enzyme, and is important in processivity.