THE CONTRIBUTION OF RECOMBINATIONDEPENDENT MECHANISMS TO THE REPLICATION OF UV-C DAMAGED DNA

VALLERGA MB, FEDERICO MB, MANSILLA SF, SPERONI J, HABIF M, GOTTIFREDI V

Buenos Aires

Congreso; SAIB-49th Annual Meeting - Argentine Society for Biochemistry and Molecular Biology; 2013

SAIB

Exposure of cells to genotoxic stimuli causes replication forks stalling at DNA lesions, which might trigger cell death. To preserve viability, cells activate tolerance mechanisms that prevent replication fork collapse. The best understood tolerance event activated by UV light is Translesion DNA Synthesis (TLS) which aids DNA replication by recruiting specialized polymerases like pol h to DNA lesions. Another less characterized tolerance event called Template Switching (TS) relies on the homology searching capacity of the recombinogenic protein, Rad51. In this context, Rad51 facilitates the utilization of the novel DNA generated on the opposite strand as alternative template. Other recombinogenic independent functions of Rad51 have also been reported. In fact, Rad51 protects replication forks from degradation in a manner that depends on its strand invasion capacity. Weather any or all of these functions of Rad51 are required after UV-C irradiation is still unclear. Cell cycle analysis and evaluation of cells in active replication and global DNA synthesis rate revealed differential responses of cells to UV-C when depleted of Rad51 or pol h. DNA combing assays allowed to estimate individual fork speed and stability. Interestingly, post UV-C the absence of Rad51 resulted in a sharp degradation of DNA fibres, indicative of unprotected forks. Fork speed was mainly affected post UV-C in pol h depleted or Rad54 depleted cells These results show that Rad51 plays an important role in the response to UV-C damaged DNA