To restore chromatin on new DNA during replication, recycling of histones 
evicted ahead of the fork is combined with new histone deposition. The Asf1 
histone chaperone, which buffers excess histones under stress, is a key player 
in this process. Yet how histones handled by human Asf1 are modified remains 
unclear. Here we identify marks on histones H3-H4 bound to Asf1 and changes 
induced upon replication stress. In S phase, distinct cytosolic and nuclear 
Asf1b complexes show ubiquitous H4K5K12diAc and heterogeneous H3 marks, 
including K9me1, K14ac, K18ac, and K56ac. Upon acute replication arrest, the 
predeposition mark H3K9me1 and modifications typical of chromatin accumulate in 
Asf1 complexes. In parallel, ssDNA is generated at replication sites, consistent 
with evicted histones being trapped with Asf1. During recovery, histones stored 
with Asf1 are rapidly used as replication resumes. This shows that replication 
stress interferes with predeposition marking and histone recycling with 
potential impact on epigenetic stability.