Catalytic subunit of two functionally distinct, structure- specific, heterodimeric DNA endonucleases MUS81-EME1 and MUS81-EME2 that are involved in the maintenance of genome stability (PubMed:11741546, PubMed:12374758, PubMed:12686547, PubMed:12721304, PubMed:24371268, PubMed:24733841, PubMed:24813886, PubMed:35290797, PubMed:39015284). Both endonucleases have essentially the same substrate specificity though MUS81-EME2 is more active than its MUS81- EME1 counterpart. Both cleave 3'-flaps and nicked Holliday junctions, and exhibit limited endonuclease activity with 5' flaps and nicked double-stranded DNAs (PubMed:24371268, PubMed:24733841, PubMed:35290797). MUS81-EME2 which is active during the replication of DNA is more specifically involved in replication fork processing (PubMed:24813886). Replication forks frequently encounter obstacles to their passage, including DNA base lesions, DNA interstrand cross-links, difficult-to-replicate sequences, transcription bubbles, or tightly bound proteins. One mechanism for the restart of a stalled replication fork involves nucleolytic cleavage mediated by the MUS81-EME2 endonuclease. By acting upon the stalled fork, MUS81-EME2 generates a DNA double-strand break (DSB) that can be repaired by homologous recombination, leading to the restoration of an active fork (PubMed:24813886). MUS81-EME2 could also function in telomere maintenance (PubMed:24813886). MUS81-EME1, on the other hand, is active later in the cell cycle and functions in the resolution of mitotic recombination intermediates including the Holliday junctions, the four- way DNA intermediates that form during homologous recombination (PubMed:11741546, PubMed:12374758, PubMed:14617801, PubMed:15805243, PubMed:24813886). {ECO:0000269|PubMed:11741546, ECO:0000269|PubMed:12374758, ECO:0000269|PubMed:12686547, ECO:0000269|PubMed:12721304, ECO:0000269|PubMed:14617801, ECO:0000269|PubMed:15805243, ECO:0000269|PubMed:24371268, ECO:0000269|PubMed:24733841, ECO:0000269|PubMed:24813886, ECO:0000269|PubMed:35290797, ECO:0000269|PubMed:39015284}. This is the function of Ensembl gene identifier ENSG00000172732 (MUS81, MUS81 structure-specific endonuclease subunit).