An evaluation of the role of LIG4 in genomic instability and adaptive mutagenesis in Candida albicans

The non-homologous end-joining (NHEJ) pathway of DNA recombination is important for genomic stability in animal cells, since the absence of Ku70, Ku80, Lig4 or Xrcc4 results in non-reciprocal translocation and chromosome fragmentation. The role of LIG4 in the genomic instability of Candida albicans has been analyzed. We have found that both cell transformation and 5'-fluoroorotic acid selection steps used to obtain several lig4 mutants (LIG4/lig4 Ura(+); LIG4/lig4 Ura(-); lig4/lig4 Ura(+); lig4/lig4 Ura(-); and revertant lig4/LIG4 Ura(+)) resulted in significant alterations in chromosome R (ChrR). However, this effect is not specific for LIG4, since disruption of SHE9, a gene unrelated to recombination, also caused alterations in the mobility of ChrR. On the other hand, we could not detect reciprocal or non-reciprocal translocations between non-homologous chromosomes in several lig4 mutants. Furthermore, propagation of these mutants in rich medium did not cause other alterations in the mobility of ChrR. Adaptive mutagenesis of C. albicans, determined by the appearance of L-sorbose-utilizing mutants on L-sorbose plates, was also independent of the presence of Lig4 and occurred by monosomy of Chr5. Accordingly, the NHEJ pathway does not appear to be involved in the adaptive mutagenesis mediated by alterations in chromosome copy number.