Deletions of immunoglobulin Cκ region characterized by the circular excision products in mouse splenocytes

Abstract

We have identified circular DNAs containing the κ light chain constant region (Cκ), as well as the excision products of Vκ-Jκ and Vλ-Jλ joining in adult mouse splenocytes. Analysis of Cκ-positive circular DNA clones revealed two recombination sites (intron recombining sequence [IRS]1 and -2) within the germline Jκ-Cκ intron region and the recombining sequence (RS) located downstream of the Cκ exon. While RS contains a conserved heptamer and nonamer separated by a 23-bp spacer on the 5′ side, IRS1 sequence is an isolated heptamer without an obvious nonamer, and IRS2 contains a variant heptamer, CACAAAA. Since IRS1 and IRS2 recombined with both RS (23-bp spacer signal) and Vκ (12-bp spacer signal) with significant frequency intron recombination sites seem to have dual recombination signals. These findings provide direct evidence that Cκ deletion preceding λ gene rearrangement can occur by looping out and excision. Increased accessibility of inefficient recombinational loci within the intron may enable recombinase to accept wide signal sequence variation.