The absence of F-box motif Encoding Gene SAF1 and Chromatin Associated factor CTF8 together contributes to MMS Resistant and HU Sensitive phenotype in S. cerevisiae

The Replication factor-C compex which related to cohesion, constitutes, three subunits called Ctf18, Ctf8 and Dcc1. These three subunit complex assist the loading of PCNA onto the chromosome. None of the replication factor C components are essential for cell viability. The null mutant of the CTF8 in S.cerevisiae shows the chromosome instability and high frequency of chromosome loss. The SAF1 gene product of S. cerevisiae involved in the degradation of adenine deaminase factor Aah1p by SCF-E3 ligase, which itself is the part of E3 ligase. The ubiquitin marked degradation of Aah1p occurs during nutrient stress which lead to cell enter into the quiescent state. The N-terminus of Saf1p interacts with the Skp1 of SCF-E3 ligase and at C-terminus recruits with Aah1p. Here we have investigated about the binary genetic interaction between the SAF1 and CTF8 genes. The strains containing single and double gene deletions of SAF1 and CTF8 were constructed in the BY4741 genetic background. Further the mutant strains were evaluated for growth fitness, genome stability and response to genotoxic stress caused by hydroxyurea (HU) and methyl methane sulfonate (MMS). The saf1Δctf8Δ strain showed the increased growth phenotype in comparison to saf1Δ, ctf8Δ, and WT strain on YPD medium. However saf1Δctf8Δ strain when grown in the presence MMS showed resistance and HU sensitive phenotype when compared with saf1Δ, ctf8Δ. The frequency of Ty1 retro-transposition was also elevated in saf1Δctf8Δ in comparison to either saf1Δ or ctf8Δ. The number of cells showing the two or multi-nuclei phenotype was also increased in saf1Δctf8Δ cells when compared with the either saf1Δ or ctf8Δ. Based on these observations, we report that the absence of both the gene SAF1 and CTF8 together leads to MMS resistance, HU sensitivity, and genome instability. This report warrants the investigation of mechanisms of differential growth phenotype due to loss of SAF1 and CTF8 together in presence of genotoxic stress in future.