Synovial Sarcoma, X Breakpoint 4 (SSX4)

SSX4, represents the more telomeric copy. Two transcript variants encoding distinct isoforms have been identified for this gene.SSX4 encodes a deduced 188-amino acid protein that shares approximately 80% sequence identity with SSX1, SSX2, SSX3, and SSX5. The SSX4 gene undergoes alternative splicing, yielding a variant product that lacks exon 5. SSX4 was strongly expressed in 1 of 12 melanoma cell lines tested.Two of the tumors were positive with either the SSX1 or the SSX2 primers, and 1 was positive with both RT-PCR assays. The third specimen showed an 187-bp fragment with 100% homology to the SYT gene linked to a 246-bp fragment with 100% homology to the long splice variant of SSX4. The breakpoint on SSX4 was identical to that observed for SSX1 and SSX2; all of the SSX genes involved in the SYT-SSX fusion genes are split between the fourth and fifth exons.