The genomic DNA region that contains the SM50 gene also included a second g
ene that appeared to encode another skeletogenic matrix protein. The two ge
nes were linked at a distance of about 12 kb. Based on the molecular weight
of the implied protein the gene was termed SM37. The SM37 protein included
a long tandem sequence of short glycine-rich repeats that was similar to t
he glycine-rich repeats included in the SM50 protein and several other skel
etal matrix proteins, although the sequence of SM37 repeat was distinct. Th
e overall structure of the SM37 protein was similar to SM50 as well. Howeve
r, SM37 was only about 30% identical in amino acid sequence to SM50, and co
ding region probes behaved as a single copy sequence under standard conditi
ons. The SM37 gene included the same cia-regulatory elements as the SM50 ge
ne, although in a different order with respect to transcription. This gene
was regulated coordinately with SM50 during development, and like SM50 was
expressed exclusively in skeletogenic mesenchyme lineages.