A Checkpoint-Related Function of the MCM Replicative Helicase Is Required to Avert Accumulation of RNA:DNA Hybrids during S-phase and Ensuing DSBs during G2/M

The mcm2-7 complex is the catalytic core of the eukaryotic replicative helicase. here,we identify a new role for this complex in maintaining genome integrity. using both genetic and cytological approaches,we find that a specific mcm allele (mcm2denq) causes elevated genome instability that correlates with the appearance of numerous dna-damage associated foci of γh2ax and rad52. we further find that the triggering events for this genome instability are elevated levels of rna:dna hybrids and an altered dna topological state,as over-expression of either rnaseh (an enzyme specific for degradation of rna in rna:dna hybrids) or topoisomerase 1 (an enzyme that relieves dna supercoiling) can suppress the mcm2denq dna-damage phenotype. moreover,the observed dna damage has several additional unusual properties,in that dna damage foci appear only after s-phase,in g2/m,and are dependent upon progression into metaphase. in addition,we show that the resultant dna damage is not due to spontaneous s-phase fork collapse. in total,these unusual mcm2denq phenotypes are markedly similar to those of a special previously-studied allele of the checkpoint sensor kinase atr/mec1,suggesting a possible regulatory interplay between mcm2-7 and atr during unchallenged growth. as rna:dna hybrids primarily result from transcription perturbations,we suggest that surveillance-mediated modulation of the mcm2-7 activity plays an important role in preventing catastrophic conflicts between replication forks and transcription complexes. possible relationships among these effects and the recently discovered role of mcm2-7 in the dna replication checkpoint induced by hu treatment are discussed. © 2016 vijayraghavan et al.