Fig. 2.

Growth delays or cell cycle arrests are caused by Ku overexpression in different strains. (A) Ku overexpression delays cell growth or arrests the cell cycle in wild-type or pif1-m2 strains, respectively. Pif1 overexpression either in the yku70 or the yku80 strains also arrests the cell cycle. The S phase cell cycle arrest in the pif1-m2 strain by Ku overexpression was abolished by the rad24 mutation. (B) FACS analysis demonstrates that Ku overexpression in the wild-type strain did not change the cell cycle profile. However, Ku overexpression in the pif1-m2 strain arrests the cell cycle in S phase. The rescue of cell cycle arrest in the pif1-m2 strain with Ku overexpression by the rad24 mutation was also confirmed by FACS analysis. (C) Northern blot analysis of HUG1 showed slight mRNA level increase by Ku overexpression, in contrast to the steady expression of β-actin. In contrast, there was no noticeable phosphorylation of Rad53 was observed by Ku overexpression although the phosphorylation of Rad53 was enhanced by MMS treatment. WT, wild type; Control, control plasmids, pYES3CT and pRS425, transformed. A protein name indicated in parentheses represents the protein overexpressed in the strain written in front of it. “+” and “−” represent the presence and absence of MMS treatment. The two major populations in the FACS analysis represented as black indicate G₁ and G₂/M populations. The FACS profile of pik1-m2 rad24Δ (yku70-yku80) shows one major population presented as black, and its DNA contents represent the S phase.