The staphylokinase gene is located in the structural gene encoding N-acetylmuramyl-L-alanine amidase in methicillin-resistant Staphylococcus aureus.

The nucleotide sequence of a 15600-bp DNA fragment containing the staphylokinase gene (sakNU3-1) of methicillin-resistant Staphylococcus aureus (MRSA) NU3-1 was determined. The sak gene was found within the ply gene encoding N-acetylmuramyl-L-alanine amidase and thus the ply gene should be inactivated. In the flanking region of the sak gene, the tandem repeat sequences (GAAGTGTT and GAATGGTT) were present as possible junction points between the sak and ply genes. No sequences characteristic of the presence of an IS-like element were found. Upstream from the ply gene, the kdpA, kdpB and kdpC homologues were present. Downstream from the ply gene, the tagA, tagH and tagG homologues were present. The sak gene was inserted into the same position of ply in 5/6 of sak(+) MRSA isolates with different genotypes. In all of these sak(+) isolates, Sak was detected in the culture supernatant.