Organization and expression of the lambda-like genes that contribute to the mu-psi light chain complex in human pre-B cells.

Lambda-like genes encode a polypeptide chain that associates with VpreB and mu chain in the so-called mu-psi light chain complex specifically expressed in pre-B cells. In humans, the lambda-like gene cluster contains three genes, termed 14.1, 16.1, and F lambda 1. The 14.1 gene contains three exons and was previously sequenced. The 16.1 and F lambda 1 have been isolated from cosmid libraries. They both contain only the exons 2 and 3 that appear highly homologous to their 14.1 counterparts. The lambda-like gene cluster has been mapped on chromosome 22, close and distal to the BCR gene, in the order (14.1; F lambda 1) and 16.1. Hybridization with the 14.1 exon 1 probe did not detect an equivalent on 16.1 and F lambda 1 genes, but instead, only revealed the X6 gene, that was previously identified 5 kb upstream of the IGLC locus. It appears, therefore, that the gene organization of the lambda and lambda-like loci is strikingly similar, with a three-exon-containing gene 5' of a series of J lambda-C lambda or J lambda-C lambda-like tandemly organized genes. Analysis of the transcripts in a 8 week old human fetal liver clearly indicated that 14.1 was the only functional gene of the lambda-like cluster. Various forms of transcripts resulting from alternate splicing have been characterized. The major component consisted of a full-length (exons 1-2-3) mRNA, whereas a minor (1-3) transcript was identified. Only the full-length transcript could encode a functional polypeptide chain corresponding to the 22 kDa light chain surrogate.