he consequences of arrest can be catastrophic if the gene being transcribed is essential as no product will be made by the arrested polymerase, and that same enzyme will cause a roadblock to other polymerases attempting to transcribe the same gene.The cell has machinery that removes the arrested polymerase and at the same time recruits repair enzymes (in particular, the endonuclease Uvr(A)BC); the repair that follows is called transcription-coupled repair. Both polymerase removal and repair enzyme recruitment are performed by a single protein called TRCF.

#Id: 7702

#Unit 1. Structure and Function of Biomolecules

                                                             Omega loop

#Id: 7704

#Unit 1. Structure and Function of Biomolecules

                                                           Loops and Turn

Small loops with regular hydrogen bond pattern and specific dihedral angles are termed as turns

#Id: 7705

#Unit 1. Structure and Function of Biomolecules

                                                               β-turns

Most common turns, also termed as ẞ-bends, tight turns, reverse turns, generally connects

β-sheets.

The conformation of i+1 and i+2 are crucial and on the basis of this, they are classified

Consists of 4 amino acids, generally termed as i, i + 1 , i + 2 and i + 3

H-bond is seen between i and i+3 (First and Fourth residue)

#Id: 7706

#Unit 1. Structure and Function of Biomolecules

                                                                                                Type I β turn

#Id: 7707

#Unit 1. Structure and Function of Biomolecules

H bonding i-i+3, i+1 in BS while i+2 in below LHH which virtually not allowed region

for most of amino acid except Gly that is why Gly is most conserved in type II B turns

                                                                Type II β turn

#Id: 7708

#Unit 1. Structure and Function of Biomolecules

                  Type l'β turn