Molecular basis for DNA repair synthesis on short gaps by mycobacterial Primase-Polymerase C

Area of Science:

• Molecular Biology
• Structural Biology
• Genomics

Background:

• Cells rely on Primase-Polymerase (Prim-Pol) enzymes for genome stability.
• Mycobacteria possess multiple Prim-Pols crucial for DNA repair pathways.
• Prim-PolC specifically handles short gap repair synthesis during excision repair.

Purpose of the Study:

• To investigate the molecular mechanisms of Prim-PolC's gap recognition and synthesis.
• To elucidate the structural basis for Prim-PolC's function in DNA repair.

Main Methods:

• X-ray crystallography was used to determine the structures of pre- and post-catalytic complexes.
• Complexes were formed with gapped DNA substrates to capture functional intermediates.

Main Results:

• Crystal structures revealed Prim-PolC's preference for short DNA gaps.
• A novel mechanism, Synthesis-dependent Template Displacement (STD), was identified.
• STD facilitates ordered insertion of templating bases into the active site during primer extension.

Conclusions:

• The study establishes the molecular basis for Prim-PolC's gap recognition and synthesis.
• The findings illuminate the unique STD mechanism employed by Prim-PolC.
• This work provides insights into the primer extension strategies of related Prim-Pol enzymes.