Pap1+ confers microtubule damage resistance to mut2a, an extragenic suppressor of the rad26:4A allele in S. pombe

The DNA structure checkpoint protein Rad26ATRIP is also required for an interphase microtubule damage response. This checkpoint delays spindle pole body separation and entry into mitosis following treatment of cells with microtubule poisons. This checkpoint requires cytoplasmic Rad26ATRIP, which is compromised by the rad26:4A allele that inhibits cytoplasmic accumulation of Rad26ATRIP following microtubule damage. The rad26::4a allele also disrupts minichromosome stability and cellular morphology, suggesting that the interphase microtubule damage checkpoint pathway operates in an effort to maintain chromosome stability and proper cell shape. To identify other proteins of the Rad26-dependent interphase microtubule damage response, we used ultra violet (UV) radiation to identify extragenic interaction suppressors of the rad26::4A growth defect on microtubule poisons. One suppressor mutation, which we named mut2a, permitted growth of rad26:4A cells on MBC media and conferred sensitivity to a microtubulin poison upon genetic outcross. In an attempt to clone this interaction suppressor using a genomic library complementation strategy, we instead isolated pap1+as an extracopy suppressor of the mut2a growth defect. We discuss the mechanism by which pap1+ overexpression may allow growth of mut2a cells in conditions that destabilize microtubules.