01% and 200 J/m2 respectively (Figure 6). However, the KU70-deficient strain showed no obvious growth defects under DNA Damage inhibitor normal growth conditions and its cell morphology was indistinguishable from WT. In addition, there were no significant differences in sugar consumption
rate and fatty acid profile between WT and ∆ku70 (Additional file 3). Figure 6 Sensitivity selleckchem of WT (top) and KU70 -deficient strain (bottom) to DNA damaging agents. An initial cell suspension of OD600 = 1.0 was serially diluted 10 folds for four times and spotted on YPD agar plates containing 0.01% MMS (v/v, upper panel) or subjected to 200 J/m2UV irradiation (bottom panel). Top panel shows the non-treated control. All plates were incubated at 28°C for 3 days. GDC 0032 molecular weight Discussion With more than 60% GC content, the KU70 and KU80 characterized here present the most GC-rich genes in the NHEJ-pathway reported so far. In terms of gene structure, both genes contain much higher density of introns than those of Y. lipolytica (Table 1), which is the best-studied oleaginous yeast to date. Not surprisingly, homologues of C. neoformans, which is under the same Basidiomycota phylum, also have
high density of introns (Table 1). DSB repair can differ in heterochromatic and euchromatic regions of the genome and histone modifying factors play an important role in this process [28, 29]. Recombination frequencies are known to vary in different genes even when assayed with the same technique and in the same genetic background . Impairment of the NHEJ-pathway has proved
to be effective in improving homologous recombination frequency in many eukaryotic hosts. However, the magnitude of improvement appears to vary considerably in different reports. With a homology sequence of approximately 750 bp, the CAR2 deletion frequency was improved 7.2-fold, from 10.5%, in WT to 75.3% in the KU70-deficient mutant in R. toruloides. This is similar to the deletion of TRP1 in Y. lipolytica although substantially higher knockout frequencies have been reported for several genes in other fungi, for example, N. crassa, A. niger and C. neoformans (Additional file 4). Nevertheless, the R. toruloides STE20 gene remained very difficult to knockout even with the ∆ku70e mutant (Table 2). This demonstrates Bumetanide a positional effect and implies additional factors that regulate gene deletion in R. toruloides. As the STE20 gene is located between the mating type loci RHA2 and RHA3 in R. toruloides, it is possible that the gene is within a transcriptionally silenced chromatin as was reported for the mating type genes in a number of other fungi [31, 32]. The low deletion frequency of STE20 suggests a potential role of chromatin structure and/or gene expression level in regulating DNA recombination in R. toruloides. One of the drawbacks of NHEJ-deficient strains is its elevated sensitivity to DNA damage and the possibility of generating unwanted mutations .