THE GENE ENCODING A MAJOR COMPONENT OF THE LATERAL ELEMENTS OF SYNAPTONEMAL COMPLEXES OF THE RAT IS RELATED TO X-LINKED LYMPHOCYTE-REGULATED GENES

The lateral elements of synaptonemal complexes (SCs) of the rat contai n major components with relative electrophoretic mobilities (M(r)S) of 30,000 and 33,000. After one-dimensional separation of SC proteins on polyacrylamide-sodium dodecyl sulfate gels, these components show up as two broad bands. These bands contain closely related proteins, as j udged from their peptide maps and immunological reactivity. Using affi nity-purified polyclonal anti-30,000 and anti-33,000-M(r) component an tibodies, we isolated a cDNA encoding at least one of the 30,000- or 3 3,000-M(r) SC components. The protein predicted from the nucleotide se quence of the cDNA, called SCP3 (for synaptoneal complex protein 3), h as a molecular mass of 29.7 kDa and a pi value of 9.4. it has a potent ial nucleotide binding site and contains stretches that are predicted to be capable of forming coiled-coil structures. In the male rat, the gene encoding SCP3 is transcribed exclusively in the testis. SCP3 has significant amino acid similarity to the pM1 protein, which is one of the predicted products of an X-linked lymphocyte-regulated gene family of the mouse: there are 63% amino acid sequence similarity and 35% am ino acid identity between the SCP3 and pM1 proteins. However, SCP3 dif fers from pM1 in several respects, and whether the proteins fulfill re lated functions is still an open question.