Regulation of RAG-2 protein expression in avian thymocytes

V(D)J recombination frequency is affected by the sequence interposed between a pair of recombination signals: sequence comparison reveals a putative recombinational enhancer element

The immunoglobulin heavy chain intron enhancer (Emu) not only stimulates transcription but also V(D)J recombination of chromosomally integrated recombination substrates. We aimed at reproducing this effect in recombination competent cells by transient transfection of extrachromosomal substrates. These we prepared by interposing between the recombination signal sequences (RSS) of the plasmid pBlueRec various fragments, including Emu, possibly affecting V(D)J recombination. Our work shows that sequences inserted between RSS 23 and RSS 12, with distances from their proximal ends of 26 and 284 bp respectively, can markedly affect the frequency of V(D)J recombination. We report that the entire Emu, the Emu core as well as its flanking 5' and 3' matrix associated regions (5' and 3' MARs) upregulate V(D)J recombination while the downstream section of the 3' MAR of Emu does not. Also, prokaryotic sequences markedly suppress V(D)J recombination. This confirms previous results obtained with chromosomally integrated substrates, except for the finding that the full length 3' MAR of Emu stimulates V(D)J recombination in an episomal but not in a chromosomal context. The fact that other MARs do not share this activity suggests that the effect is no mediated through attachment of the recombination substrate to a nuclear matrix-associated recombination complex but through cis-activation. The presence of a 26 bp A-T-rich sequence motif in the 5' and 3' MARs of Emu and in all of the other upregulating fragments investigated, leads us to propose that the motif represents a novel recombinational enhancer element distinct from those constituting the Emu core.

rag-1 and rag-2 are components of a high-molecular-weight complex, and association of rag-2 with this complex is rag-1 dependent

Despite the essential and synergistic functions of the rag-1 and rag-2 proteins in V(D)J recombination and lymphocyte development, little is known about the biochemical properties of the two proteins. We have developed cell lines expressing high levels of the rag proteins and specific, sensitive immunological reagents for their detection, and we have examined the physical properties of the rag proteins in vitro and their subcellular localizations in vivo. rag-1 is tightly associated with nuclear structures, requires a high salt concentration to maintain its solubility, and is a component of large, heterogeneously sized complexes. Furthermore, the presence of rag-1 alters the behavior of rag-2, conferring on it properties similar to those of rag-1 and changing its distribution in the nucleus. We demonstrate that rag-1 and rag-2 are present in the same complex by coimmunoprecipitation, and we provide evidence that these complexes contain more molecules of rag-2 than of rag-1. The demonstration of intracellular complexes containing rag-1 and rag-2 raises the possibility that interaction between these proteins is necessary for their biological function.