SCP2 - A MAJOR PROTEIN-COMPONENT OF THE AXIAL ELEMENTS OF SYNAPTONEMAL COMPLEXES OF THE RAT

In the axial elements of synaptonemal complexes (SCs) of the rat, majo r protein components have been identified, with relative electrophoret ic mobilities (M(r)s) of 30 000-33 000 and 190 000. Using monoclonal a nti-SC antibodies, we isolated cDNA fragments which encode the 190 000 M-r component of rat SCs, The translation product predicted from the nucleotide sequence of the cDNA, called SCP2 (for synaptonemal complex protein 2), is a basic protein (pl = 8.0) with a molecular mass of 17 3 kDa, At the C-terminus, a stretch of similar to 50 amino acid residu es is predicted to be capable of forming coiled-coil structures. SCP2 contains two clusters of S/T-P motifs, which are common in DNA-binding proteins. These clusters flank the central, most basic part of the pr otein (pl = 9.5). Three of the Sla-P motifs are potential target sites for p34(cdc2) protein kinase, In addition, SCP2 has eight potential c AMP/cGMP-dependent protein kinase target sites. The gene encoding SCP2 is transcribed specifically in the testis, In meiotic prophase cells. At the amino acid sequence and secondary structural level, SCP2 shows some similarity to the Red1 protein, which is involved in meiotic rec ombination and the assembly of axial elements of SCs in yeast. We spec ulate that SCP2 is a DNA-binding protein involved in the structural or ganization of meiotic prophase chromosomes.