Substrate targeting component of a cullin-RING-based E3 ubiquitin-protein ligase complex RTT101(MMS1-MMS22). RTT101(MMS1-MMS22) promotes fork progression through damaged DNA or natural pause sites by stabilizing replication proteins like the replication fork-pausing complex (FPC) and leading-strand polymerase at stalled replication forks. RTT101(MMS1-MMS22) ubiquitinates the acetylated histones H3K56ac-H4 at lysine residues H3K121, H3K122 and H3K125. Ubiquitination is required for efficient histone deposition during replication-coupled nucleosome assembly, probably by facilitating the transfer of H3-H4 from ASF1 to other chaperones involved in histone deposition. Component of a cullin-RING ligase (CRL) composed of 4 subunits: the RING protein HRT1, the cullin RTT101, a linker protein MMS1, and the substrate receptor MMS22. This complex further interacts with RTT107 and CTF4 to form RTT101-MMS1-MMS22-RTT107 and RTT101-MMS1-MMS22-CTF4 complexes respectively. Interacts (via C-ter) with MMS1 (via N-ter). Interacts with RTT107. Nuclear punctate foci structures. Belongs to the MMS22 family.