Identical 3' non-coding sequences in five mouse Ig kappa chain mRNAs favour a unique C kappa gene.

Abstract

The constant regions of immunoglobulin κ chains are encoded by a very small but unknown number of genes. The kinetics of nucleic acid reassociation is consistent with up to four Cκ genes per haploid mouse genome1–4, while saturation hybridisation suggests that there are two Cκ genes5. The amino acid sequences proposed for seven κ C regions do differ slightly6–10, but at least some of these differences result from sequencing errors11. Determining the nucleotide sequence of the C region of κ mRNAs11 and the adjacent 3′ non-coding region should more readily reveal any slight differences reflecting a multiplicity of Cκ genes. Examination of the 3′ non-coding region may be particularly useful, as this region is not constrained to encode the largely invariant Cκ amino acid sequence. Sequences reported for the 3′ terminal regions of two κ mRNAs, MOPC 21 (refs 11, 12) and MOPC 41A (ref. 13), were identical for the first 59 residues, but the subsequent, tentative, 45 residues proposed for MOPC 41A mRNA differed from the MOPC 21 sequence. It was unclear, however, whether these differences resulted from methodological problems, or genuine sequence divergence. We have therefore re-examined the MOPC 41A 3′ terminal sequence in a direct comparison with that of MOPC 21 and also determined 3′ terminal sequences of about 100 residues in three other κ mRNAs. We confirm here the sequence presented by Hamlyn et al.11 for the MOPC 21 mRNA and show that not only the MOPC 41A mRNA, but also the three other κ mRNAs have the same sequence.